blocks|key|998503|text|最简单的方法(如果您不担心特殊的Unicode字符)是调用toUpperCase|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|998504|var+areEqual+=+string1.toUpperCase()+===+string2.toUpperCase();|code-block|syntax|javascript|998505|entityMap^0|T|B|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

The simplest way to do it (if you're not worried about special Unicode characters) is to call <code>toUpperCase</code>:

<pre><code>var areEqual = string1.toUpperCase() === string2.toUpperCase();
</code></pre>

blocks|key|765850|text|：这个答案最初是9年前添加的。现在，您应该使用带有sensitivity:+'accent'选项的localeCompare：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|765851|​|765852|function+ciEquals(a,+b)+{
++++return+typeof+a+===+'string'+&&+typeof+b+===+'string'
++++++++?+a.localeCompare(b,+undefined,+{+sensitivity:+'accent'+})+===+0
++++++++:+a+===+b;
}

console.log("'a'+=+'a'?",+ciEquals('a',+'a'));
console.log("'AaA'+=+'aAa'?",+ciEquals('AaA',+'aAa'));
console.log("'a'+=+'á'?",+ciEquals('a',+'á'));
console.log("'a'+=+'b'?",+ciEquals('a',+'b'));|code-block|syntax|javascript|765853|765854|{+sensitivity:+'accent'+}告诉localeCompare()将相同基本字母的两个变体视为相同，除非它们具有不同的口音(如上面的第三个示例所示)。|765855|或者，您也可以使用{+sensitivity:+'base'+}，只要两个字符的基本字符相同，它就会将这两个字符视为等效字符(因此，A将被视为与á等效)。|765856|请注意，localeCompare的第三个参数在IE10或更低版本或某些移动浏览器中不受支持(请参阅上面链接的页面上的兼容性图表)，因此如果您需要支持这些浏览器，您将需要某种后备：|BOLD|765857|function+ciEqualsInner(a,+b)+{
++++return+a.localeCompare(b,+undefined,+{+sensitivity:+'accent'+})+===+0;
}

function+ciEquals(a,+b)+{
++++if+(typeof+a+!==+'string'+%7C%7C+typeof+b+!==+'string')+{
++++++++return+a+===+b;
++++}

++++//++++++v---+feature+detection
++++return+ciEqualsInner('A',+'a')
++++++++?+ciEqualsInner(a,+b)
++++++++:+/*++fallback+approach+here++*/;
}|765858|原始答案|765859|在JavaScript中执行不区分大小写的比较的最佳方法是使用带有i标志的RegExp+match()方法。|765860|Case-insensitive+search|765861|当被比较的两个字符串都是变量(而不是常量)时，这就有点复杂了，因为您需要从字符串生成一个RegExp，但是如果字符串中包含特殊的正则表达式字符，则将字符串传递给RegExp构造函数可能会导致不正确的匹配或失败的匹配。|765862|如果您关心国际化，那么不要使用toLowerCase()或toUpperCase()，因为它们并不能在所有语言中提供准确的、不区分大小写的比较。|765863|http://www.i18nguy.com/unicode/turkish-i18n.html|765864|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare|1|https://stackoverflow.com/questions/177719/javascript-case-insensitive-search|2^0|P|L|1D|D|1D|D|0|0|0|0|0|0|P|R|F|0|9|N|1U|1|20|1|0|0|3|4|D|0|0|0|X|1|18|7|0|0|N|1|0|0|F|D|T|D|0|0|1C|2|0^^$0|@$1|2|3|4|5|6|7|1J|8|@$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]]|D|@$9|1O|A|1P|1|1Q]]|E|$]]|$1|F|3|G|5|6|7|1R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1S|8|@]|D|@]|E|$K|L]]|$1|M|3|G|5|6|7|1T|8|@]|D|@]|E|$]]|$1|N|3|O|5|6|7|1U|8|@$9|1V|A|1W|B|C]|$9|1X|A|1Y|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1Z|8|@$9|20|A|21|B|C]|$9|22|A|23|B|C]|$9|24|A|25|B|C]]|D|@]|E|$]]|$1|R|3|S|5|6|7|26|8|@$9|27|A|28|B|T]|$9|29|A|2A|B|C]]|D|@]|E|$]]|$1|U|3|V|5|J|7|2B|8|@]|D|@]|E|$K|L]]|$1|W|3|X|5|6|7|2C|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|6|7|2D|8|@$9|2E|A|2F|B|C]|$9|2G|A|2H|B|C]]|D|@]|E|$]]|$1|10|3|11|5|6|7|2I|8|@]|D|@$9|2J|A|2K|1|2L]]|E|$]]|$1|12|3|13|5|6|7|2M|8|@]|D|@]|E|$]]|$1|14|3|15|5|6|7|2N|8|@$9|2O|A|2P|B|C]|$9|2Q|A|2R|B|C]]|D|@]|E|$]]|$1|16|3|17|5|6|7|2S|8|@]|D|@$9|2T|A|2U|1|2V]]|E|$]]|$1|18|3|-4|5|6|7|2W|8|@]|D|@]|E|$]]]|19|$1A|$5|1B|1C|1D|E|$1E|1F]]|1G|$5|1B|1C|1D|E|$1E|1H]]|1I|$5|1B|1C|1D|E|$1E|17]]]]

EDIT: This answer was originally added 9 years ago. Today you should use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare" rel="noreferrer"><code>localeCompare</code></a> with the <code>sensitivity: 'accent'</code> option:

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>function ciEquals(a, b) {
 return typeof a === 'string' &amp;&amp; typeof b === 'string'
 ? a.localeCompare(b, undefined, { sensitivity: 'accent' }) === 0
 : a === b;
}

console.log("'a' = 'a'?", ciEquals('a', 'a'));
console.log("'AaA' = 'aAa'?", ciEquals('AaA', 'aAa'));
console.log("'a' = 'á'?", ciEquals('a', 'á'));
console.log("'a' = 'b'?", ciEquals('a', 'b'));</code></pre>
</div>
</div>


The <code>{ sensitivity: 'accent' }</code> tells <code>localeCompare()</code> to treat two variants of the same base letter as the same unless they have different accents (as in the third example) above.

Alternatively, you can use <code>{ sensitivity: 'base' }</code>, which treats two characters as equivalent as long as their base character is the same (so <code>A</code> would be treated as equivalent to <code>á</code>).

Note that the third parameter of <code>localeCompare</code> is not supported in IE10 or lower or certain mobile browsers (see the compatibility chart on the page linked above), so if you need to support those browsers, you'll need some kind of fallback:

<pre><code>function ciEqualsInner(a, b) {
 return a.localeCompare(b, undefined, { sensitivity: 'accent' }) === 0;
}

function ciEquals(a, b) {
 if (typeof a !== 'string' || typeof b !== 'string') {
 return a === b;
 }

 // v--- feature detection
 return ciEqualsInner('A', 'a')
 ? ciEqualsInner(a, b)
 : /* fallback approach here */;
}
</code></pre>

Original answer

The best way to do a case insensitive comparison in JavaScript is to use RegExp <code>match()</code> method with the <code>i</code> flag. 

<a href="https://stackoverflow.com/questions/177719/javascript-case-insensitive-search">Case-insensitive search</a>

When both strings being compared are variables (not constants), then it's a little more complicated 'cause you need to generate a RegExp from the string but passing the string to RegExp constructor can result in incorrect matches or failed matches if the string has special regex characters in it.

If you care about internationalization don't use <code>toLowerCase()</code> or <code>toUpperCase()</code> as it doesn't provide accurate case-insensitive comparisons in all languages.

<a href="http://www.i18nguy.com/unicode/turkish-i18n.html" rel="noreferrer">http://www.i18nguy.com/unicode/turkish-i18n.html</a>

blocks|key|17848|text|我写了一个扩展。非常琐碎|type|unstyled|depth|inlineStyleRanges|entityRanges|data|17849|if+(typeof+String.prototype.isEqual!=+'function')+{
++++String.prototype.isEqual+=+function+(str){
++++++++return+this.toUpperCase()==str.toUpperCase();
+++++};
}|code-block|syntax|javascript|17850|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I wrote a extension. very trivial

<pre><code>if (typeof String.prototype.isEqual!= 'function') {
 String.prototype.isEqual = function (str){
 return this.toUpperCase()==str.toUpperCase();
 };
}
</code></pre>

blocks|key|765888|text|更新：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|765889|根据评论，之前的答案检查source+contains+keyword，以使其平等检查添加了%5E和$。|offset|length|style|CODE|765890|(/%5Ekeyword$/i).test(source)|code-block|syntax|javascript|765891|765892|在正则表达式的帮助下我们也可以实现。|765893|(/keyword/i).test(source)|765894|/i用于忽略大小写。如果没有必要，我们可以忽略并测试不区分大小写的匹配，比如|765895|(/keyword/).test(source)|765896|entityMap^0|0|C|N|1A|1|1C|1|0|0|0|0|0|0|2|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@$D|Z|E|10|F|G]|$D|11|E|12|F|G]|$D|13|E|14|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|15|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|17|8|@]|9|@]|A|$]]|$1|P|3|Q|5|J|7|18|8|@]|9|@]|A|$K|L]]|$1|R|3|S|5|6|7|19|8|@$D|1A|E|1B|F|G]]|9|@]|A|$]]|$1|T|3|U|5|J|7|1C|8|@]|9|@]|A|$K|L]]|$1|V|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]]|W|$]]

<h3>Update:</h3>
As per the comments, previous answer checks for <code>source contains keyword</code>, to make it equality check added <code>^</code> and <code>$</code>.
<pre class="lang-js prettyprint-override"><code>(/^keyword$/i).test(source)
</code></pre>
<hr />
With the help of regular expression also we can achieve.
<pre><code>(/keyword/i).test(source)
</code></pre>
<code>/i</code> is for ignoring case. If not necessary we can ignore and test for NOT case sensitive matches like
<pre><code>(/keyword/).test(source)
</code></pre>

blocks|key|765384|text|请记住，大小写是特定于区域设置的操作。根据场景的不同，您可能需要考虑这一点。例如，如果您正在比较两个人的姓名，您可能希望考虑地区设置，但如果您正在比较机器生成的值，例如UUID，则可能不会。这就是为什么我在我的utils库中使用以下函数的原因(请注意，由于性能原因，不包括类型检查)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|765385|function+compareStrings+(string1,+string2,+ignoreCase,+useLocale)+{
++++if+(ignoreCase)+{
++++++++if+(useLocale)+{
++++++++++++string1+=+string1.toLocaleLowerCase();
++++++++++++string2+=+string2.toLocaleLowerCase();
++++++++}
++++++++else+{
++++++++++++string1+=+string1.toLowerCase();
++++++++++++string2+=+string2.toLowerCase();
++++++++}
++++}

++++return+string1+===+string2;
}|code-block|syntax|javascript|765386|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Remember that casing is a locale specific operation. Depending on scenario you may want to take that in to account. For example, if you are comparing names of two people you may want to consider locale but if you are comparing machine generated values such as UUID then you might not. This why I use following function in my utils library (note that type checking is not included for performance reason).

<pre><code>function compareStrings (string1, string2, ignoreCase, useLocale) {
 if (ignoreCase) {
 if (useLocale) {
 string1 = string1.toLocaleLowerCase();
 string2 = string2.toLocaleLowerCase();
 }
 else {
 string1 = string1.toLowerCase();
 string2 = string2.toLowerCase();
 }
 }

 return string1 === string2;
}
</code></pre>

blocks|key|998681|text|如果你关心不等式的方向(也许你想对列表进行排序)，你必须进行大小写转换，并且由于unicode中的小写字符比大写字符多，toLowerCase可能是最好的转换。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|998682|function+my_strcasecmp(+a,+b+)+
{
++++if((a%2B'').toLowerCase()+>+(b%2B'').toLowerCase())+return+1++
++++if((a%2B'').toLowerCase()+<+(b%2B'').toLowerCase())+return+-1
++++return+0
}|code-block|syntax|javascript|998683|Javascript似乎使用区域设置"C“进行字符串比较，因此如果字符串包含ASCII以外的字母，那么结果的顺序将会很糟糕。如果不对字符串进行更详细的检查，我们对此无能为力。|998684|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

if you are concerned about the direction of the inequality (perhaps you want to sort a list)
you pretty-much have to do case-conversion, and as there are more lowercase characters in unicode than uppercase toLowerCase is probably the best conversion to use.

<pre><code>function my_strcasecmp( a, b ) 
{
 if((a+'').toLowerCase() &gt; (b+'').toLowerCase()) return 1 
 if((a+'').toLowerCase() &lt; (b+'').toLowerCase()) return -1
 return 0
}
</code></pre>

Javascript seems to use locale "C" for string comparisons so the resulting ordering will
be ugly if the strings contain other than ASCII letters. there's not much that can be done about that without doing much more detailed inspection of the strings.

blocks|key|17707|text|不区分大小写的比较有两种方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|17708|17709|将字符串转换为大写，然后使用严格运算符(===)对它们进行比较。严格运算符如何处理操作数读取内容:使用字符串方法进行http://www.thesstech.com/javascript/relational-logical-operators|ordered-list-item|offset|length|style|CODE|17710|Pattern匹配：|17711|17712|使用search字符串方法进行不区分大小写的搜索。有关搜索和其他字符串方法的信息，请访问：http://www.thesstech.com/pattern-matching-using-string-methods|17713|<!doctype+html>
++<html>
++++<head>
++++++<script>

++++++++//+1st+way

++++++++var+a+=+"apple";
++++++++var+b+=+"APPLE";++
++++++++if+(a.toUpperCase()+===+b.toUpperCase())+{
++++++++++alert("equal");
++++++++}

++++++++//2nd+way

++++++++var+a+=+"+Null+and+void";
++++++++document.write(a.search(/null/i));+

++++++</script>
++++</head>
</html>|code-block|syntax|javascript|17714|entityMap|0|LINK|mutability|MUTABLE|url|http://www.thesstech.com/javascript/relational-logical-operators|1|http://www.thesstech.com/pattern-matching-using-string-methods^0|0|0|K|3|1M|1S|0|0|0|0|19|1Q|1|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|14|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|15|8|@$F|16|G|17|H|I]]|9|@$F|18|G|19|1|1A]]|A|$]]|$1|J|3|K|5|E|7|1B|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1D|8|@]|9|@$F|1E|G|1F|1|1G]]|A|$]]|$1|O|3|P|5|Q|7|1H|8|@]|9|@]|A|$R|S]]|$1|T|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|U|$V|$5|W|X|Y|A|$Z|10]]|11|$5|W|X|Y|A|$Z|12]]]]

There are two ways for case insensitive comparison:

<ol>
<li>Convert strings to upper case and then compare them using the strict operator (<code>===</code>). How strict operator treats operands read stuff at:
<a href="http://www.thesstech.com/javascript/relational-logical-operators" rel="noreferrer">http://www.thesstech.com/javascript/relational-logical-operators</a></li>
<li>Pattern matching using string methods:</li>
</ol>

Use the "search" string method for case insensitive search.
Read about search and other string methods at:
<a href="http://www.thesstech.com/pattern-matching-using-string-methods" rel="noreferrer">http://www.thesstech.com/pattern-matching-using-string-methods</a> 

<pre><code>&lt;!doctype html&gt;
 &lt;html&gt;
 &lt;head&gt;
 &lt;script&gt;

 // 1st way

 var a = "apple";
 var b = "APPLE"; 
 if (a.toUpperCase() === b.toUpperCase()) {
 alert("equal");
 }

 //2nd way

 var a = " Null and void";
 document.write(a.search(/null/i)); 

 &lt;/script&gt;
 &lt;/head&gt;
&lt;/html&gt;
</code></pre>

blocks|key|2408074|text|甚至这个问题也已经回答了。我有一种不同的方法来使用RegExp和match来忽略区分大小写。请查看我的链接https://jsfiddle.net/marchdave/7v8bd7dq/27/|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|2408075|$("#btnGuess").click(guessWord);

++function+guessWord()+{

+++var+letter+=+$("#guessLetter").val();
+++var+word+=+'ABC';
+++var+pattern+=+RegExp(letter,+'gi');+//+pattern:+/a/gi

+++var+result+=+word.match(pattern);
+++alert('Ignore+case+sensitive:'+%2B+result);

++}|code-block|syntax|javascript|2408076|entityMap|0|LINK|mutability|MUTABLE|url|https://jsfiddle.net/marchdave/7v8bd7dq/27/^0|1H|17|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Even this question have already answered. I have a different approach to use RegExp and match to ignore case sensitive. Please see my link 
<a href="https://jsfiddle.net/marchdave/7v8bd7dq/27/" rel="nofollow">https://jsfiddle.net/marchdave/7v8bd7dq/27/</a>

<pre><code>$("#btnGuess").click(guessWord);

 function guessWord() {

 var letter = $("#guessLetter").val();
 var word = 'ABC';
 var pattern = RegExp(letter, 'gi'); // pattern: /a/gi

 var result = word.match(pattern);
 alert('Ignore case sensitive:' + result);

 }
</code></pre>

blocks|key|2408111|text|我最近创建了一个微库，它提供不区分大小写的字符串帮助器：https://github.com/nickuraltsev/ignore-case。(它在内部使用toUpperCase。)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2408112|var+ignoreCase+=+require('ignore-case');

ignoreCase.equals('FOO',+'Foo');+//+=>+true
ignoreCase.startsWith('foobar',+'FOO');+//+=>+true
ignoreCase.endsWith('foobar',+'BaR');+//+=>+true
ignoreCase.includes('AbCd',+'c');+//+=>+true
ignoreCase.indexOf('AbCd',+'c');+//+=>+2|code-block|syntax|javascript|2408113|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/nickuraltsev/ignore-case^0|27|B|S|17|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

I have recently created a micro library that provides case-insensitive string helpers: <a href="https://github.com/nickuraltsev/ignore-case" rel="noreferrer">https://github.com/nickuraltsev/ignore-case</a>. (It uses <code>toUpperCase</code> internally.)

<pre><code>var ignoreCase = require('ignore-case');

ignoreCase.equals('FOO', 'Foo'); // =&gt; true
ignoreCase.startsWith('foobar', 'FOO'); // =&gt; true
ignoreCase.endsWith('foobar', 'BaR'); // =&gt; true
ignoreCase.includes('AbCd', 'c'); // =&gt; true
ignoreCase.indexOf('AbCd', 'c'); // =&gt; 2
</code></pre>

blocks|key|766001|text|假设我们想要在字符串变量haystack中找到字符串变量needle。有三个陷阱：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|766002|766003|Internationalized应用程序应该避免使用string.toUpperCase和string.toLowerCase。改用忽略大小写的正则表达式。例如，var+needleRegExp+=+new+RegExp(needle,+"i");后跟needleRegExp.test(haystack).|ordered-list-item|766004|In+general，您可能不知道needle的值。注意，needle不包含任何正则表达式special+characters。如果您想精确匹配needle和haystack，忽略大小写，请确保在正则表达式constructor.|766005|的开头添加"%5E"，在结尾添加"$"|766006|考虑到第(1)点和第(2)点，示例如下：|766007|var+haystack+=+"A.+BAIL.+Of.+Hay.";
var+needle+=+"bail.";
var+needleRegExp+=+new+RegExp(needle.replace(/[-[\]{}()*%2B?.,\\%5E$%7C#\s]/g,+"\\$&"),+"i");
var+result+=+needleRegExp.test(haystack);
if+(result)+{
++++//+Your+code+here
}|code-block|syntax|javascript|766008|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions?redirectlocale=en-US&redirectslug=JavaScript%252FGuide%252FRegular_Expressions^0|C|8|S|6|0|0|R|I|1A|I|2A|17|3J|R|0|H|6|T|6|20|6|27|8|19|I|0|0|5|3|E|3|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|G|3|H|5|I|7|18|8|@$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]|$9|1F|A|1G|B|C]]|D|@]|E|$]]|$1|J|3|K|5|I|7|1H|8|@$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]|$9|1O|A|1P|B|C]]|D|@$9|1Q|A|1R|1|1S]]|E|$]]|$1|L|3|M|5|6|7|1T|8|@$9|1U|A|1V|B|C]|$9|1W|A|1X|B|C]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1Y|8|@]|D|@]|E|$]]|$1|P|3|Q|5|R|7|1Z|8|@]|D|@]|E|$S|T]]|$1|U|3|-4|5|6|7|20|8|@]|D|@]|E|$]]]|V|$W|$5|X|Y|Z|E|$10|11]]]]

Suppose we want to find the string variable <code>needle</code> in the string variable <code>haystack</code>. There are three gotchas:

<ol>
<li>Internationalized applications should avoid <code>string.toUpperCase</code> and <code>string.toLowerCase</code>. Use a regular expression which ignores case instead. For example, <code>var needleRegExp = new RegExp(needle, "i");</code> followed by <code>needleRegExp.test(haystack)</code>.</li>
<li>In general, you might not know the value of <code>needle</code>. Be careful that <code>needle</code> does not contain any regular expression <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions?redirectlocale=en-US&amp;redirectslug=JavaScript%2FGuide%2FRegular_Expressions" rel="noreferrer">special characters</a>. Escape these using <code>needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&amp;");</code>.</li>
<li>In other cases, if you want to precisely match <code>needle</code> and <code>haystack</code>, just ignoring case, make sure to add <code>"^"</code> at the start and <code>"$"</code> at the end of your regular expression constructor.</li>
</ol>

Taking points (1) and (2) into consideration, an example would be: 

<pre><code>var haystack = "A. BAIL. Of. Hay.";
var needle = "bail.";
var needleRegExp = new RegExp(needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&amp;"), "i");
var result = needleRegExp.test(haystack);
if (result) {
 // Your code here
}
</code></pre>

blocks|key|998822|text|如果不抛出异常，不使用慢速正则表达式呢？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|998823|return+str1+!=+null+&&+str2+!=+null+
++++&&+typeof+str1+===+'string'+&&+typeof+str2+===+'string'
++++&&+str1.toUpperCase()+===+str2.toUpperCase();|code-block|syntax|javascript|998824|上面的代码片段假设您不希望匹配任何一个字符串为空或未定义的字符串。|998825|如果要匹配null/undefined，则：|998826|return+(str1+==+null+&&+str2+==+null)
++++%7C%7C+(str1+!=+null+&&+str2+!=+null+
++++++++&&+typeof+str1+===+'string'+&&+typeof+str2+===+'string'
++++++++&&+str1.toUpperCase()+===+str2.toUpperCase());|998827|如果出于某种原因，您关心未定义的vs+null：|998828|return+(str1+===+undefined+&&+str2+===+undefined)
++++%7C%7C+(str1+===+null+&&+str2+===+null)
++++%7C%7C+(str1+!=+null+&&+str2+!=+null+
++++++++&&+typeof+str1+===+'string'+&&+typeof+str2+===+'string'
++++++++&&+str1.toUpperCase()+===+str2.toUpperCase());|998829|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

How about NOT throwing exceptions and NOT using slow regex?

<pre><code>return str1 != null &amp;&amp; str2 != null 
 &amp;&amp; typeof str1 === 'string' &amp;&amp; typeof str2 === 'string'
 &amp;&amp; str1.toUpperCase() === str2.toUpperCase();
</code></pre>

The above snippet assumes you don't want to match if either string is null or undefined.

If you want to match null/undefined, then:

<pre><code>return (str1 == null &amp;&amp; str2 == null)
 || (str1 != null &amp;&amp; str2 != null 
 &amp;&amp; typeof str1 === 'string' &amp;&amp; typeof str2 === 'string'
 &amp;&amp; str1.toUpperCase() === str2.toUpperCase());
</code></pre>

If for some reason you care about undefined vs null:

<pre><code>return (str1 === undefined &amp;&amp; str2 === undefined)
 || (str1 === null &amp;&amp; str2 === null)
 || (str1 != null &amp;&amp; str2 != null 
 &amp;&amp; typeof str1 === 'string' &amp;&amp; typeof str2 === 'string'
 &amp;&amp; str1.toUpperCase() === str2.toUpperCase());
</code></pre>

blocks|key|2408164|text|str+=+'Lol',+str2+=+'lOl',+regex+=+new+RegExp('%5E'+%2B+str+%2B+'$',+'i');
if+(regex.test(str))+{
++++console.log("true");
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2408165|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>str = 'Lol', str2 = 'lOl', regex = new RegExp('^' + str + '$', 'i');
if (regex.test(str)) {
 console.log("true");
}
</code></pre>

blocks|key|2408201|text|这里有很多答案，但我想添加一个基于扩展字符串lib的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2408202|String.prototype.equalIgnoreCase+=+function(str)
{
++++return+(str+!=+null+
++++++++++++&&+typeof+str+===+'string'
++++++++++++&&+this.toUpperCase()+===+str.toUpperCase());
}|code-block|syntax|javascript|2408203|这样你就可以像在Java中一样使用它了！|2408204|示例：|2408205|var+a+=+"hello";
var+b+=+"HeLLo";
var+c+=+"world";

if+(a.equalIgnoreCase(b))+{
++++document.write("a+==+b");
}
if+(a.equalIgnoreCase(c))+{
++++document.write("a+==+c");
}
if+(!b.equalIgnoreCase(c))+{
++++document.write("b+!=+c");
}|2408206|输出将为：|2408207|"a+==+b"
"b+!=+c"|2408208|​|2408209|String.prototype.equalIgnoreCase+=+function(str)+{
++return+(str+!=+null+&&
++++typeof+str+===+'string'+&&
++++this.toUpperCase()+===+str.toUpperCase());
}


var+a+=+"hello";
var+b+=+"HeLLo";
var+c+=+"world";

if+(a.equalIgnoreCase(b))+{
++document.write("a+==+b");
++document.write(" ");
}
if+(a.equalIgnoreCase(c))+{
++document.write("a+==+c");
}
if+(!b.equalIgnoreCase(c))+{
++document.write("b+!=+c");
}|2408210|2408211|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Z|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|10|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|12|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|14|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|U|3|R|5|6|7|16|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|W|$]]

Lots of answers here, but I like to add a sollution based on extending the String lib:

<pre><code>String.prototype.equalIgnoreCase = function(str)
{
 return (str != null 
 &amp;&amp; typeof str === 'string'
 &amp;&amp; this.toUpperCase() === str.toUpperCase());
}
</code></pre>

This way you can just use it like you do in Java!

Example:

<pre><code>var a = "hello";
var b = "HeLLo";
var c = "world";

if (a.equalIgnoreCase(b)) {
 document.write("a == b");
}
if (a.equalIgnoreCase(c)) {
 document.write("a == c");
}
if (!b.equalIgnoreCase(c)) {
 document.write("b != c");
}
</code></pre>

Output will be:

<pre><code>"a == b"
"b != c"
</code></pre>

<div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>String.prototype.equalIgnoreCase = function(str) {
 return (str != null &amp;&amp;
 typeof str === 'string' &amp;&amp;
 this.toUpperCase() === str.toUpperCase());
}


var a = "hello";
var b = "HeLLo";
var c = "world";

if (a.equalIgnoreCase(b)) {
 document.write("a == b");
 document.write("&lt;br&gt;");
}
if (a.equalIgnoreCase(c)) {
 document.write("a == c");
}
if (!b.equalIgnoreCase(c)) {
 document.write("b != c");
}</code></pre>
</div>
</div>

blocks|key|2408244|text|由于没有明确提供使用RegExp的简单代码片段，下面是我的尝试：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2408245|function+compareInsensitive(str1,+str2){+
++return+typeof+str1+===+'string'+&&+
++++typeof+str2+===+'string'+&&+
++++new+RegExp("%5E"+%2B+str1.replace(/[-\/\\%5E$*%2B?.()%7C[\]{}]/g,+'\\$&')+%2B+"$",+"i").test(str2);
}|code-block|syntax|javascript|2408246|它有几个优点：|2408247|str1.toUpperCase()).|2408248|Does字符串验证参数类型(任何非字符串参数，如undefined，都会使类似于|unordered-list-item|2408249|+not+possible+internationalization+issues.|ordered-list-item|2408250|Escapes+RegExp+string的表达式崩溃。|2408251|2408252|2408253|entityMap^0|A|6|0|0|0|0|I|0|O|9|0|0|8|6|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|O|3|P|5|Q|7|18|8|@$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|R|3|S|5|T|7|1B|8|@]|D|@]|E|$]]|$1|U|3|V|5|T|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]|$1|X|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|Z|$]]

Since no answer clearly provided a simple code snippet for using <code>RegExp</code>, here's my attempt:

<pre><code>function compareInsensitive(str1, str2){ 
 return typeof str1 === 'string' &amp;&amp; 
 typeof str2 === 'string' &amp;&amp; 
 new RegExp("^" + str1.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\$&amp;') + "$", "i").test(str2);
}
</code></pre>

It has several advantages:

<ol>
<li>Verifies parameter type (any non-string parameter, like <code>undefined</code> for example, would crash an expression like <code>str1.toUpperCase()</code>).</li>
<li>Does not suffer from possible internationalization issues.</li>
<li>Escapes the <code>RegExp</code> string.</li>
</ol>

blocks|key|998916|text|使用RegEx进行字符串匹配或比较。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|998917|在JavaScript中，您可以使用match()进行字符串比较，但不要忘记将i放在RegEx中。|offset|length|style|CODE|998918|示例：|998919|var+matchString+=+"Test";
if+(matchString.match(/test/i))+{
++alert('String+matched');
}
else+{
+alert('String+not+matched');
}|code-block|syntax|javascript|998920|entityMap^0|0|I|7|13|1|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]|$D|U|E|V|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|W|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|X|8|@]|9|@]|A|$M|N]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Use RegEx for string match or comparison.

In JavaScript, you can use <code>match()</code> for string comparison,
don't forget to put <code>i</code>in RegEx.

Example:

<pre><code>var matchString = "Test";
if (matchString.match(/test/i)) {
 alert('String matched');
}
else {
 alert('String not matched');
}
</code></pre>

blocks|key|766078|text|如果这两个字符串具有相同的已知区域设置，则可能需要使用Intl.Collator对象，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|766079|function+equalIgnoreCase(s1:+string,+s2:+string)+{
++++return+new+Intl.Collator("en-US",+{+sensitivity:+"base"+}).compare(s1,+s2)+===+0;
}|code-block|syntax|javascript|766080|显然，您可能希望缓存Collator以获得更高的效率。|766081|这种方法的优点是，它应该比使用RegExps快得多，并且基于一组非常可定制的(请参阅上面文章中对locales和options构造函数参数的描述)现成的排序器。|766082|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Collator^0|R|D|R|D|0|0|0|A|8|0|1C|7|1K|7|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|1B|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

If both strings are of the same known locale, you may want to use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Collator" rel="nofollow noreferrer"><code>Intl.Collator</code></a> object like this:

<pre><code>function equalIgnoreCase(s1: string, s2: string) {
 return new Intl.Collator("en-US", { sensitivity: "base" }).compare(s1, s2) === 0;
}
</code></pre>

Obviously, you may want to cache the <code>Collator</code> for better efficiency.

The advantages of this approach is that it should be much faster than using RegExps and is based on an extremely customizable (see description of <code>locales</code> and <code>options</code> constructor parameters in the article above) set of ready-to-use collators.

blocks|key|2408414|text|正如在最近的评论中所说，string::localeCompare支持不区分大小写的比较(以及其他强大的功能)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2408415|下面是一个简单的例子|2408416|'xyz'.localeCompare('XyZ',+undefined,+{+sensitivity:+'base'+});+//+returns+0|code-block|syntax|javascript|2408417|和一个你可以使用的泛型函数|2408418|function+equalsIgnoringCase(text,+other)+{
++++return+text.localeCompare(other,+undefined,+{+sensitivity:+'base'+})+===+0;
}|2408419|请注意，您可能应该输入您正在使用的特定区域设置，而不是undefined。正如MDN文档中所指出的，这一点很重要|2408420|瑞典语中的|2408421|、ä和a是单独的基本字母|blockquote|2408422|2408423|2408424|敏感度选项|2408425|​|2408426|📷|atomic|2408427|2408428|浏览器支持|2408429|截至发帖时，适用于Android和Opera+Mini的UC浏览器不支持区域设置和选项参数。请查看https://caniuse.com/#search=localeCompare以获取最新信息。|2408430|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare|1|IMAGE|IMMUTABLE|imageUrl|https://i.stack.imgur.com/tTMud.png|imageAlt|2|https://caniuse.com/#search=localeCompare^0|C|L|C|L|0|0|0|0|0|0|R|9|0|0|0|0|0|0|0|0|1|1|0|0|0|1D|15|2|0^^$0|@$1|2|3|4|5|6|7|1R|8|@$9|1S|A|1T|B|C]]|D|@$9|1U|A|1V|1|1W]]|E|$]]|$1|F|3|G|5|6|7|1X|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1Y|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|20|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|21|8|@$9|22|A|23|B|C]]|D|@]|E|$]]|$1|S|3|T|5|6|7|24|8|@]|D|@]|E|$]]|$1|U|3|V|5|W|7|25|8|@]|D|@]|E|$]]|$1|X|3|-4|5|6|7|26|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|27|8|@]|D|@]|E|$]]|$1|Z|3|10|5|6|7|28|8|@]|D|@]|E|$]]|$1|11|3|12|5|6|7|29|8|@]|D|@]|E|$]]|$1|13|3|14|5|15|7|2A|8|@]|D|@$9|2B|A|2C|1|2D]]|E|$]]|$1|16|3|12|5|6|7|2E|8|@]|D|@]|E|$]]|$1|17|3|18|5|6|7|2F|8|@]|D|@]|E|$]]|$1|19|3|1A|5|6|7|2G|8|@]|D|@$9|2H|A|2I|1|2J]]|E|$]]|$1|1B|3|-4|5|6|7|2K|8|@]|D|@]|E|$]]]|1C|$1D|$5|1E|1F|1G|E|$1H|1I]]|1J|$5|1K|1F|1L|E|$1M|1N|1O|-4]]|1P|$5|1E|1F|1G|E|$1H|1Q]]]]

As said in recent comments, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/localeCompare" rel="noreferrer"><code>string::localeCompare</code></a> supports case insensitive comparisons (among other powerful things).

Here's a simple example

<pre><code>'xyz'.localeCompare('XyZ', undefined, { sensitivity: 'base' }); // returns 0
</code></pre>

And a generic function you could use

<pre><code>function equalsIgnoringCase(text, other) {
 return text.localeCompare(other, undefined, { sensitivity: 'base' }) === 0;
}
</code></pre>

Note that instead of <code>undefined</code> you should probably enter the specific locale you are working with. This is important as denoted in the MDN docs

<blockquote>
 in Swedish, ä and a are separate base letters
</blockquote>

<h2>Sensitivity options</h2>

<a href="https://i.stack.imgur.com/tTMud.png" rel="noreferrer"><img src="https://i.stack.imgur.com/tTMud.png" alt="Sensitivity options tabulated from MDN"></a>

<h2>Browser support</h2>

As of time of posting, UC Browser for Android and Opera Mini do not support locale and options parameters. Please check <a href="https://caniuse.com/#search=localeCompare" rel="noreferrer">https://caniuse.com/#search=localeCompare</a> for up to date info.

blocks|key|17892|text|这是this+answer的改进版。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|17893|String.equal+=+function+(s1,+s2,+ignoreCase,+useLocale)+{
++++if+(s1+==+null+%7C%7C+s2+==+null)
++++++++return+false;

++++if+(!ignoreCase)+{
++++++++if+(s1.length+!==+s2.length)
++++++++++++return+false;

++++++++return+s1+===+s2;
++++}

++++if+(useLocale)+{
++++++++if+(useLocale.length)
++++++++++++return+s1.toLocaleLowerCase(useLocale)+===+s2.toLocaleLowerCase(useLocale)
++++++++else
++++++++++++return+s1.toLocaleLowerCase()+===+s2.toLocaleLowerCase()
++++}
++++else+{
++++++++if+(s1.length+!==+s2.length)
++++++++++++return+false;

++++++++return+s1.toLowerCase()+===+s2.toLowerCase();
++++}
}|code-block|syntax|javascript|17894|17895|用法和测试：|17896|​|17897|17898|String.equal+=+function+(s1,+s2,+ignoreCase,+useLocale)+{
++++if+(s1+==+null+%7C%7C+s2+==+null)
++++++++return+false;

++++if+(!ignoreCase)+{
++++++++if+(s1.length+!==+s2.length)
++++++++++++return+false;

++++++++return+s1+===+s2;
++++}

++++if+(useLocale)+{
++++++++if+(useLocale.length)
++++++++++++return+s1.toLocaleLowerCase(useLocale)+===+s2.toLocaleLowerCase(useLocale)
++++++++else
++++++++++++return+s1.toLocaleLowerCase()+===+s2.toLocaleLowerCase()
++++}
++++else+{
++++++++if+(s1.length+!==+s2.length)
++++++++++++return+false;

++++++++return+s1.toLowerCase()+===+s2.toLowerCase();
++++}
}

//+If+you+don't+mind+extending+the+prototype.
String.prototype.equal+=+function(string2,+ignoreCase,+useLocale)+{
++return+String.equal(this.valueOf(),+string2,+ignoreCase,+useLocale);
}

//+------------------+TESTS+----------------------
console.log("Tests...");

console.log('Case+sensitive+1');
var+result+=+"Abc123".equal("Abc123");
console.assert(result+===+true);

console.log('Case+sensitive+2');
result+=+"aBC123".equal("Abc123");
console.assert(result+===+false);

console.log('Ignore+case');
result+=+"AbC123".equal("aBc123",+true);
console.assert(result+===+true);

console.log('Ignore+case+%2B+Current+locale');
result+=+"AbC123".equal("aBc123",+true);
console.assert(result+===+true);

console.log('Turkish+test+1+(ignore+case,+en-US)');
result+=+"IiiI".equal("ıiİI",+true,+"en-US");
console.assert(result+===+false);

console.log('Turkish+test+2+(ignore+case,+tr-TR)');
result+=+"IiiI".equal("ıiİI",+true,+"tr-TR");
console.assert(result+===+true);

console.log('Turkish+test+3+(case+sensitive,+tr-TR)');
result+=+"IiiI".equal("ıiİI",+false,+"tr-TR");
console.assert(result+===+false);

console.log('null-test-1');
result+=+"AAA".equal(null);
console.assert(result+===+false);

console.log('null-test-2');
result+=+String.equal(null,+"BBB");
console.assert(result+===+false);

console.log('null-test-3');
result+=+String.equal(null,+null);
console.assert(result+===+false);|17899|17900|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/20318795/1844247^0|E|3|2|B|0|0|0|0|0|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]]|E|$]]|$1|F|3|G|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|18|8|@]|D|@]|E|$]]|$1|L|3|M|5|6|7|19|8|@$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1C|8|@]|D|@]|E|$]]|$1|P|3|O|5|6|7|1D|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|S|3|O|5|6|7|1F|8|@]|D|@]|E|$]]|$1|T|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|U|$V|$5|W|X|Y|E|$Z|10]]]]

This is an improved version of <a href="https://stackoverflow.com/a/20318795/1844247">this answer</a>.

<pre><code>String.equal = function (s1, s2, ignoreCase, useLocale) {
 if (s1 == null || s2 == null)
 return false;

 if (!ignoreCase) {
 if (s1.length !== s2.length)
 return false;

 return s1 === s2;
 }

 if (useLocale) {
 if (useLocale.length)
 return s1.toLocaleLowerCase(useLocale) === s2.toLocaleLowerCase(useLocale)
 else
 return s1.toLocaleLowerCase() === s2.toLocaleLowerCase()
 }
 else {
 if (s1.length !== s2.length)
 return false;

 return s1.toLowerCase() === s2.toLowerCase();
 }
}
</code></pre>

 
<hr/>
Usages &amp; tests:

<div class="snippet" data-lang="js" data-hide="true" data-console="true" data-babel="false">
<div class="snippet-code snippet-currently-hidden">
<pre class="snippet-code-js lang-js prettyprint-override"><code>String.equal = function (s1, s2, ignoreCase, useLocale) {
 if (s1 == null || s2 == null)
 return false;

 if (!ignoreCase) {
 if (s1.length !== s2.length)
 return false;

 return s1 === s2;
 }

 if (useLocale) {
 if (useLocale.length)
 return s1.toLocaleLowerCase(useLocale) === s2.toLocaleLowerCase(useLocale)
 else
 return s1.toLocaleLowerCase() === s2.toLocaleLowerCase()
 }
 else {
 if (s1.length !== s2.length)
 return false;

 return s1.toLowerCase() === s2.toLowerCase();
 }
}

// If you don't mind extending the prototype.
String.prototype.equal = function(string2, ignoreCase, useLocale) {
 return String.equal(this.valueOf(), string2, ignoreCase, useLocale);
}

// ------------------ TESTS ----------------------
console.log("Tests...");

console.log('Case sensitive 1');
var result = "Abc123".equal("Abc123");
console.assert(result === true);

console.log('Case sensitive 2');
result = "aBC123".equal("Abc123");
console.assert(result === false);

console.log('Ignore case');
result = "AbC123".equal("aBc123", true);
console.assert(result === true);

console.log('Ignore case + Current locale');
result = "AbC123".equal("aBc123", true);
console.assert(result === true);

console.log('Turkish test 1 (ignore case, en-US)');
result = "IiiI".equal("ıiİI", true, "en-US");
console.assert(result === false);

console.log('Turkish test 2 (ignore case, tr-TR)');
result = "IiiI".equal("ıiİI", true, "tr-TR");
console.assert(result === true);

console.log('Turkish test 3 (case sensitive, tr-TR)');
result = "IiiI".equal("ıiİI", false, "tr-TR");
console.assert(result === false);

console.log('null-test-1');
result = "AAA".equal(null);
console.assert(result === false);

console.log('null-test-2');
result = String.equal(null, "BBB");
console.assert(result === false);

console.log('null-test-3');
result = String.equal(null, null);
console.assert(result === false);</code></pre>
</div>
</div>

blocks|key|766148|text|将两者转换为较低的字符串(出于性能原因，仅转换一次)，并将其与内联三元运算符进行比较：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|766149|function+strcasecmp(s1,s2){
++++s1=(s1%2B'').toLowerCase();
++++s2=(s2%2B'').toLowerCase();
++++return+s1>s2?1:(s1<s2?-1:0);
}|code-block|syntax|javascript|766150|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Convert both to lower string (only once for performance reasons) and compare them with inline ternary operator:
<pre><code>function strcasecmp(s1,s2){
 s1=(s1+'').toLowerCase();
 s2=(s2+'').toLowerCase();
 return s1&gt;s2?1:(s1&lt;s2?-1:0);
}
</code></pre>

blocks|key|17938|text|如果您知道您正在处理ascii文本，那么您可以只使用大小写字符偏移量比较。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|17939|只需确保你的“完美”字符串(你想要匹配的字符串)是小写的：|17940|const+CHARS_IN_BETWEEN+=+32;
const+LAST_UPPERCASE_CHAR+=+90;+//+Z
function+strMatchesIgnoreCase(lowercaseMatch,+value)+{
++++let+i+=+0,+matches+=+lowercaseMatch.length+===+value.length;
++++while+(matches+&&+i+<+lowercaseMatch.length)+{
++++++++const+a+=+lowercaseMatch.charCodeAt(i);
++++++++const+A+=+a+-+CHARS_IN_BETWEEN;
++++++++const+b+=+value.charCodeAt(i);
++++++++const+B+=+b+%2B+((b+>+LAST_UPPERCASE_CHAR)+?+-CHARS_IN_BETWEEN+:+CHARS_IN_BETWEEN);
++++++++matches+=+a+===+b+//+lowerA+===+b
++++++++++++%7C%7C+A+===+b+//+upperA+==+b
++++++++++++%7C%7C+a+===+B+//+lowerA+==+~b
++++++++++++%7C%7C+A+===+B;+//+upperA+==+~b
++++++++i%2B%2B;
++++}
++++return+matches;
}|code-block|syntax|javascript|17941|entityMap^0|A|5|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

If you know you're dealing with <code>ascii</code> text then you can just use a uppercase/lowercase character offset comparison.

Just make sure the string your "perfect" string (the one you want to match against) is lowercase:

<pre class="lang-js prettyprint-override"><code>const CHARS_IN_BETWEEN = 32;
const LAST_UPPERCASE_CHAR = 90; // Z
function strMatchesIgnoreCase(lowercaseMatch, value) {
 let i = 0, matches = lowercaseMatch.length === value.length;
 while (matches &amp;&amp; i &lt; lowercaseMatch.length) {
 const a = lowercaseMatch.charCodeAt(i);
 const A = a - CHARS_IN_BETWEEN;
 const b = value.charCodeAt(i);
 const B = b + ((b &gt; LAST_UPPERCASE_CHAR) ? -CHARS_IN_BETWEEN : CHARS_IN_BETWEEN);
 matches = a === b // lowerA === b
 || A === b // upperA == b
 || a === B // lowerA == ~b
 || A === B; // upperA == ~b
 i++;
 }
 return matches;
}
</code></pre>

blocks|key|2408544|text|我喜欢这个速记变体-|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2408545|export+const+equalsIgnoreCase+=+(str1,+str2)+=>+{
++++return+(!str1+&&+!str2)+%7C%7C+(str1+&&+str2+&&+str1.toUpperCase()+==+str2.toUpperCase())
}|code-block|syntax|javascript|2408546|处理速度快，并且可以做它想做的事情。|2408547|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I like this quick shorthand variation - 

<pre><code>export const equalsIgnoreCase = (str1, str2) =&gt; {
 return (!str1 &amp;&amp; !str2) || (str1 &amp;&amp; str2 &amp;&amp; str1.toUpperCase() == str2.toUpperCase())
}
</code></pre>

Quick in processing, and does what it is intended to.

blocks|key|18133|text|为了获得更好的浏览器兼容性，您可以依赖正则表达式。这将适用于过去20年发布的所有web浏览器：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|18134|String.prototype.equalsci+=+function(s)+{
++++var+regexp+=+RegExp("%5E"%2Bthis.replace(/[.\\%2B*?\[\%5E\]$(){}=!<>%7C:-]/g,+"\\$&")%2B"$",+"i");
++++return+regexp.test(s);
}

"PERSON@Ü.EXAMPLE.COM".equalsci("person@ü.example.com")//+returns+true|code-block|syntax|javascript|18135|这与这里找到的其他答案不同，因为它考虑到并非所有用户都在使用现代web浏览器。|18136|注意:如果你需要支持像土耳其语这样的特殊情况，你需要使用localeCompare，因为我和我在土耳其语中不是同一个字母。|18137|"I".localeCompare("i",+undefined,+{+sensitivity:"accent"})===0//+returns+true
"I".localeCompare("i",+"tr",+{+sensitivity:"accent"})===0//+returns+false|18138|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

For better browser compatibility you can rely on a regular expression. This will work in all web browsers released in the last 20 years:
<pre><code>String.prototype.equalsci = function(s) {
 var regexp = RegExp(&quot;^&quot;+this.replace(/[.\\+*?\[\^\]$(){}=!&lt;&gt;|:-]/g, &quot;\\$&amp;&quot;)+&quot;$&quot;, &quot;i&quot;);
 return regexp.test(s);
}

&quot;PERSON@Ü.EXAMPLE.COM&quot;.equalsci(&quot;person@ü.example.com&quot;)// returns true
</code></pre>
This is different from the other answers found here because it takes into account that not all users are using modern web browsers.
Note: If you need to support unusual cases like the Turkish language you will need to use localeCompare because i and I are not the same letter in Turkish.
<pre><code>&quot;I&quot;.localeCompare(&quot;i&quot;, undefined, { sensitivity:&quot;accent&quot;})===0// returns true
&quot;I&quot;.localeCompare(&quot;i&quot;, &quot;tr&quot;, { sensitivity:&quot;accent&quot;})===0// returns false
</code></pre>

blocks|key|18144|text|我们也可以使用ASCII来做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|18145|function+toLower(a){

++++let+c+=+"";

++++
++++for(let+i+=+0;i<a.length;i%2B%2B){

++++++++
++++++++let+f+=+a.charCodeAt(i);
++++++++if(f+<+95){

++++++++++++c+%2B=+String.fromCharCode(f%2B32);
++++++++}
++++++++else{

++++++++++++c+%2B=+a[i];
++++++++}
++++}

++++return+c;
}
function+compareIt(a,b){


++++return+toLower(a)==toLower(b);


}
console.log(compareIt("An+ExamPlE"+,+"an+example"));|code-block|syntax|javascript|18146|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

We could also do this using ASCII:
<pre><code>function toLower(a){

 let c = &quot;&quot;;

 
 for(let i = 0;i&lt;a.length;i++){

 
 let f = a.charCodeAt(i);
 if(f &lt; 95){

 c += String.fromCharCode(f+32);
 }
 else{

 c += a[i];
 }
 }

 return c;
}
function compareIt(a,b){


 return toLower(a)==toLower(b);


}
console.log(compareIt(&quot;An ExamPlE&quot; , &quot;an example&quot;));
</code></pre>

How do I perform case insensitive string comparison in JavaScript?

How to do case insensitive string comparison?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如何在JavaScript中进行不区分大小写的字符串比较？

问如何进行不区分大小写的字符串比较？
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问如何进行不区分大小写的字符串比较？EN