blocks|key|4612586|text|如果“有效”意味着“其中只有base64字符”，那么请检查/[A-Za-z0-9%2B/=]/。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4612587|如果“有效”意味着一个“合法的”base64编码的字符串，那么你应该在最后检查=。|4612588|如果“有效”意味着解码后它是合理的，那么它需要领域知识。|4612589|entityMap^0|T|G|0|13|1|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|R|8|@]|D|@]|E|$]]|$1|J|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|K|$]]

If "valid" means "only has base64 chars in it" then check against <code>/[A-Za-z0-9+/=]/</code>.

If "valid" means a "legal" base64-encoded string then you should check for the <code>=</code> at the end.

If "valid" means it's something reasonable after decoding then it requires domain knowledge.

blocks|key|2996926|text|如果你想检查它是否可以解码，你可以简单地尝试解码，看看是否失败：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2996927|try+{
++++window.atob(str);
}+catch(e)+{
++++//+something+failed

++++//+if+you+want+to+be+specific+and+only+catch+the+error+which+means
++++//+the+base+64+was+invalid,+then+check+for+'e.code+===+5'.
++++//+(because+'DOMException.INVALID_CHARACTER_ERR+===+5')
}|code-block|syntax|javascript|2996928|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|$]]

If you want to check whether it can be decoded or not, you can simply try decoding it and see whether it failed:

<pre><code>try {
 window.atob(str);
} catch(e) {
 // something failed

 // if you want to be specific and only catch the error which means
 // the base 64 was invalid, then check for 'e.code === 5'.
 // (because 'DOMException.INVALID_CHARACTER_ERR === 5')
}
</code></pre>

blocks|key|4612705|text|这应该能起到作用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4612706|function+isBase64(str)+{
++++if+(str+===''+%7C%7C+str.trim()+===''){+return+false;+}
++++try+{
++++++++return+btoa(atob(str))+==+str;
++++}+catch+(err)+{
++++++++return+false;
++++}
}|code-block|syntax|javascript|4612707|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|$]]

This should do the trick.

<pre><code>function isBase64(str) {
 if (str ==='' || str.trim() ===''){ return false; }
 try {
 return btoa(atob(str)) == str;
 } catch (err) {
 return false;
 }
}
</code></pre>

blocks|key|4895383|text|在@anders-marzi-tornblad's+answer基础上，使用正则表达式对base64有效性进行简单的真/假测试，就像下面这样简单：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4895384|var+base64regex+=+/%5E([0-9a-zA-Z%2B/]{4})*(([0-9a-zA-Z%2B/]{2}==)%7C([0-9a-zA-Z%2B/]{3}=))?$/;

base64regex.test("SomeStringObviouslyNotBase64Encoded...");+++++++++++++//+FALSE
base64regex.test("U29tZVN0cmluZ09idmlvdXNseU5vdEJhc2U2NEVuY29kZWQ=");+++//+TRUE|code-block|syntax|javascript|4895385|更新2021|4895386|在下面的评论之后，|4895387|透露，这个基于正则表达式的解决方案提供了比简单的检查更准确的检查，可能只有base16编码才会忽略try``ingatobbecause+the+latter+doesn't+check+for=-padding.+According+to+[RFC4648](https://datatracker.ietf.org/doc/html/rfc4648#section-5)=`-padding，或者如果数据长度已知，implicitely.|unordered-list-item|style|CODE|4895388|Regex-based解决方案似乎也是最快的，因为kai的hinted。由于jsperf看起来像是片状的自动取款机，我做了一个new+test+on+jsbench来证实这一点。|4895389|4895390|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/7860392/determine-if-string-is-in-base64-using-javascript/35002237#answer-7874175|1|https://stackoverflow.com/users/9562423/kai|2|https://stackoverflow.com/questions/7860392/determine-if-string-is-in-base64-using-javascript/35002237#answer-51302482|3|https://jsben.ch/6idLl^0|1|V|0|0|0|0|0|1D|8|1P|10|2Q|2H|0|P|3|1|T|6|2|1R|J|3|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@$A|19|B|1A|1|1B]]|C|$]]|$1|D|3|E|5|F|7|1C|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1D|8|@]|9|@]|C|$]]|$1|K|3|L|5|6|7|1E|8|@]|9|@]|C|$]]|$1|M|3|N|5|O|7|1F|8|@$A|1G|B|1H|P|Q]|$A|1I|B|1J|P|Q]|$A|1K|B|1L|P|Q]]|9|@]|C|$]]|$1|R|3|S|5|O|7|1M|8|@]|9|@$A|1N|B|1O|1|1P]|$A|1Q|B|1R|1|1S]|$A|1T|B|1U|1|1V]]|C|$]]|$1|T|3|-4|5|6|7|1W|8|@]|9|@]|C|$]]|$1|U|3|-4|5|6|7|1X|8|@]|9|@]|C|$]]]|V|$W|$5|X|Y|Z|C|$10|11]]|12|$5|X|Y|Z|C|$10|13]]|14|$5|X|Y|Z|C|$10|15]]|16|$5|X|Y|Z|C|$10|17]]]]

Building on <a href="https://stackoverflow.com/questions/7860392/determine-if-string-is-in-base64-using-javascript/35002237#answer-7874175">@anders-marzi-tornblad's answer</a>, using the regex to make a simple true/false test for base64 validity is as easy as follows:
<pre><code>var base64regex = /^([0-9a-zA-Z+/]{4})*(([0-9a-zA-Z+/]{2}==)|([0-9a-zA-Z+/]{3}=))?$/;

base64regex.test(&quot;SomeStringObviouslyNotBase64Encoded...&quot;); // FALSE
base64regex.test(&quot;U29tZVN0cmluZ09idmlvdXNseU5vdEJhc2U2NEVuY29kZWQ=&quot;); // TRUE
</code></pre>
<h3>Update 2021</h3>
<ul>
<li>Following the comments below it transpires this regex-based solution provides a more accurate check than simply <code>try</code>`ing <code>atob</code> because the latter doesn't check for <code>=</code>-padding. According to <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-5" rel="nofollow noreferrer">RFC4648</a> <code>=</code>-padding may only be ignored for base16-encoding or if the data length is known implicitely.</li>
<li>Regex-based solution also seems to be the fastest as <a href="https://stackoverflow.com/questions/7860392/determine-if-string-is-in-base64-using-javascript/35002237#answer-51302482">hinted</a> by <a href="https://stackoverflow.com/users/9562423/kai">kai</a>. As jsperf seems flaky atm i made a <a href="https://jsben.ch/6idLl" rel="nofollow noreferrer">new test on jsbench</a> which confirms this.</li>
</ul>

blocks|key|4895286|text|为此，我会使用正则表达式。试试这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4895287|/%5E([0-9a-zA-Z%2B/]{4})*(([0-9a-zA-Z%2B/]{2}==)%7C([0-9a-zA-Z%2B/]{3}=))?$/|code-block|syntax|javascript|4895288|解释：|4895289|%5E++++++++++++++++++++++++++#+Start+of+input
([0-9a-zA-Z%2B/]{4})*++++++++#+Groups+of+4+valid+characters+decode
+++++++++++++++++++++++++++#+to+24+bits+of+data+for+each+group
(++++++++++++++++++++++++++#+Either+ending+with:
++++([0-9a-zA-Z%2B/]{2}==)+++#+two+valid+characters+followed+by+==
++++%7C++++++++++++++++++++++#+,+or
++++([0-9a-zA-Z%2B/]{3}=)++++#+three+valid+characters+followed+by+=
)?+++++++++++++++++++++++++#+,+or+nothing
$++++++++++++++++++++++++++#+End+of+input|4895290|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I would use a regular expression for that. Try this one:

<pre><code>/^([0-9a-zA-Z+/]{4})*(([0-9a-zA-Z+/]{2}==)|([0-9a-zA-Z+/]{3}=))?$/
</code></pre>

Explanation:

<pre><code>^ # Start of input
([0-9a-zA-Z+/]{4})* # Groups of 4 valid characters decode
 # to 24 bits of data for each group
( # Either ending with:
 ([0-9a-zA-Z+/]{2}==) # two valid characters followed by ==
 | # , or
 ([0-9a-zA-Z+/]{3}=) # three valid characters followed by =
)? # , or nothing
$ # End of input
</code></pre>

blocks|key|2996985|text|此方法尝试解码，然后编码，并与原始文件进行比较。对于出现解析错误的环境，也可以与其他答案结合使用。从正则表达式的角度来看，也可能有一个字符串看起来像有效的base64，但不是实际的base64。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2996986|if(btoa(atob(str))==str){
++//...
}|code-block|syntax|javascript|2996987|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|$]]

This method attempts to decode then encode and compare to the original. Could also be combined with the other answers for environments that throw on parsing errors. Its also possible to have a string that looks like valid base64 from a regex point of view but is not actual base64.

<pre><code>if(btoa(atob(str))==str){
 //...
}
</code></pre>

blocks|key|2997064|text|这是我最喜欢的验证库之一的实现方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2997065|const+notBase64+=+/[%5EA-Z0-9%2B\/=]/i;

export+default+function+isBase64(str)+{
++assertString(str);+//+remove+this+line+and+make+sure+you+pass+in+a+string
++const+len+=+str.length;
++if+(!len+%7C%7C+len+%25+4+!==+0+%7C%7C+notBase64.test(str))+{
++++return+false;
++}
++const+firstPaddingChar+=+str.indexOf('=');
++return+firstPaddingChar+===+-1+%7C%7C
++++firstPaddingChar+===+len+-+1+%7C%7C
++++(firstPaddingChar+===+len+-+2+&&+str[len+-+1]+===+'=');
}|code-block|syntax|javascript|2997066|https://github.com/chriso/validator.js/blob/master/src/lib/isBase64.js|offset|length|2997067|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|0|1Y|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@$I|U|J|V|1|W]]|A|$]]|$1|K|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|H]]]]

This is how it's done in one of my favorite validation libs:

<pre><code>const notBase64 = /[^A-Z0-9+\/=]/i;

export default function isBase64(str) {
 assertString(str); // remove this line and make sure you pass in a string
 const len = str.length;
 if (!len || len % 4 !== 0 || notBase64.test(str)) {
 return false;
 }
 const firstPaddingChar = str.indexOf('=');
 return firstPaddingChar === -1 ||
 firstPaddingChar === len - 1 ||
 (firstPaddingChar === len - 2 &amp;&amp; str[len - 1] === '=');
}
</code></pre>

<a href="https://github.com/chriso/validator.js/blob/master/src/lib/isBase64.js" rel="nofollow noreferrer">https://github.com/chriso/validator.js/blob/master/src/lib/isBase64.js</a>

blocks|key|731413|text|对我来说，一个字符串很可能是一个编码的base64，如果：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|731414|731415|it的长度可被4|ordered-list-item|731416|整除|731417|+uses+A-Z+a-z+0-9+=结尾使用=+(0-3个字符)|offset|length|style|CODE|731418|731419|所以代码应该是|731420|function+isBase64(str)
{
++++return+str.length+%25+4+==+0+&&+/%5E[A-Za-z0-9%2B/]%2B[=]{0,3}$/.test(str);
}|code-block|syntax|javascript|731421|entityMap^0|0|0|0|0|6|3|A|3|E|3|I|1|N|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|Z|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|10|8|@]|9|@]|A|$]]|$1|H|3|I|5|E|7|11|8|@$J|12|K|13|L|M]|$J|14|K|15|L|M]|$J|16|K|17|L|M]|$J|18|K|19|L|M]|$J|1A|K|1B|L|M]]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1D|8|@]|9|@]|A|$]]|$1|Q|3|R|5|S|7|1E|8|@]|9|@]|A|$T|U]]|$1|V|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|W|$]]

For me a string is likely an encoded base64 if:
<ol>
<li>it's length is divisible by 4</li>
<li>uses <code>A-Z</code> <code>a-z</code> <code>0-9</code> <code>+/=</code></li>
<li>only uses <code>=</code> in the end (0-3 chars)</li>
</ol>
so the code would be
<pre class="lang-js prettyprint-override"><code>function isBase64(str)
{
 return str.length % 4 == 0 &amp;&amp; /^[A-Za-z0-9+/]+[=]{0,3}$/.test(str);
}
</code></pre>

blocks|key|4612943|text|nodejs中的实现(不仅验证允许的字符，还验证base64字符串)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4612944|++++const+validateBase64+=+function(encoded1)+{
++++++++var+decoded1+=+Buffer.from(encoded1,+'base64').toString('utf8');
++++++++var+encoded2+=+Buffer.from(decoded1,+'binary').toString('base64');
++++++++return+encoded1+==+encoded2;
++++}|code-block|syntax|javascript|4612945|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|$]]

Implementation in nodejs (validates not just allowed chars but base64 string at all)
<pre><code>
 const validateBase64 = function(encoded1) {
 var decoded1 = Buffer.from(encoded1, 'base64').toString('utf8');
 var encoded2 = Buffer.from(decoded1, 'binary').toString('base64');
 return encoded1 == encoded2;
 }

</code></pre>

blocks|key|2997162|text|我知道已经很晚了，但我试着让它变得简单；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2997163|function+isBase64(encodedString)+{
++++var+regexBase64+=+/%5E([0-9a-zA-Z%2B/]{4})*(([0-9a-zA-Z%2B/]{2}==)%7C([0-9a-zA-Z%2B/]{3}=))?$/;
++++return+regexBase64.test(encodedString);+++//+return+TRUE+if+its+base64+string.
}|code-block|syntax|javascript|2997164|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 know its late, but I tried to make it simple here;
<pre><code>function isBase64(encodedString) {
 var regexBase64 = /^([0-9a-zA-Z+/]{4})*(([0-9a-zA-Z+/]{2}==)|([0-9a-zA-Z+/]{3}=))?$/;
 return regexBase64.test(encodedString); // return TRUE if its base64 string.
}
</code></pre>

I'm using the <code>window.atob('string')</code> function to decode a string from base64 to a string. Now I wonder, is there any way to check that 'string' is actually valid base64? I would like to be notified if the string is not base64 so I can perform a different action.

Determine if string is in base64 using JavaScript

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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我使用window.atob('string')函数将字符串从base64解码为字符串。现在我想知道，有什么方法可以检查'string‘是否真的是有效的base64？如果字符串不是base64，我希望得到通知，这样我就可以执行不同的操作。

问使用JavaScript确定字符串是否在base64中
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