blocks|key|673202|text|您可以使用比较运算符来查看它是否在数字字符范围内：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673203|var+c+=+justPrices[i].substr(commapos%2B2,1);
if+(c+>=+'0'+&&+c+<=+'9')+{
++++//+it+is+a+number
}+else+{
++++//+it+isn't
}|code-block|syntax|javascript|673204|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|$]]

You could use comparison operators to see if it is in the range of digit characters:

<pre><code>var c = justPrices[i].substr(commapos+2,1);
if (c &gt;= '0' &amp;&amp; c &lt;= '9') {
 // it is a number
} else {
 // it isn't
}
</code></pre>

blocks|key|673149|text|您可以使用parseInt，然后使用isNaN进行检查|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|673150|或者，如果你想直接处理你的字符串，你可以像这样使用regexp：|673151|function+is_numeric(str){
++++return+/%5E\d%2B$/.test(str);
}|code-block|syntax|javascript|673152|entityMap^0|5|8|I|5|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

you can either use <code>parseInt</code> and than check with <code>isNaN</code>

or if you want to work directly on your string you can use regexp like this:

<pre><code>function is_numeric(str){
 return /^\d+$/.test(str);
}
</code></pre>

blocks|key|673578|text|我想知道为什么没有人发布这样的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673579|var+charCodeZero+=+"0".charCodeAt(0);
var+charCodeNine+=+"9".charCodeAt(0);

function+isDigitCode(n)+{
+++return(n+>=+charCodeZero+&&+n+<=+charCodeNine);
}|code-block|syntax|javascript|673580|使用类似这样的调用：|673581|if+(isDigitCode(justPrices[i].charCodeAt(commapos%2B2)))+{
++++...+//+digit
}+else+{
++++...+//+not+a+digit
}|673582|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 wonder why nobody has posted a solution like:

<pre><code>var charCodeZero = "0".charCodeAt(0);
var charCodeNine = "9".charCodeAt(0);

function isDigitCode(n) {
 return(n &gt;= charCodeZero &amp;&amp; n &lt;= charCodeNine);
}
</code></pre>

with an invocation like:

<pre><code>if (isDigitCode(justPrices[i].charCodeAt(commapos+2))) {
 ... // digit
} else {
 ... // not a digit
}
</code></pre>

blocks|key|673709|text|简单函数|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673710|function+isCharNumber(c)+{
++return+c+>=+'0'+&&+c+<=+'9';
}|code-block|syntax|javascript|673711|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|$]]

Simple function
<pre><code>function isCharNumber(c) {
 return c &gt;= '0' &amp;&amp; c &lt;= '9';
}
</code></pre>

blocks|key|673313|text|您可以使用以下命令：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673314|function+isDigit(n)+{
++++return+Boolean([true,+true,+true,+true,+true,+true,+true,+true,+true,+true][n]);
}|code-block|syntax|javascript|673315|在这里，我将它与公认的方法：http://jsperf.com/isdigittest/5进行了比较。我没有期望太多，所以当我发现接受的方法要慢得多时，我非常惊讶。|offset|length|673316|有趣的是，虽然被接受的方法是更快的正确输入(例如，'5')和较慢的错误(例如'a')，我的方法正好相反(快速表示不正确，较慢表示正确)。|673317|尽管如此，在最坏的情况下，我的方法对于正确的输入比接受的解决方案快2倍，对于错误的输入比接受的解决方案快5倍以上。|673318|entityMap|0|LINK|mutability|MUTABLE|url|http://jsperf.com/isdigittest/5^0|0|0|E|V|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@$I|Z|J|10|1|11]]|A|$]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

You can use this:

<pre><code>function isDigit(n) {
 return Boolean([true, true, true, true, true, true, true, true, true, true][n]);
}
</code></pre>

Here, I compared it to the accepted method: <a href="http://jsperf.com/isdigittest/5">http://jsperf.com/isdigittest/5</a> . I didn't expect much, so I was pretty suprised, when I found out that accepted method was much slower. 

Interesting thing is, that while accepted method is faster correct input (eg. '5') and slower for incorrect (eg. 'a'), my method is exact opposite (fast for incorrect and slower for correct).

Still, in worst case, my method is 2 times faster than accepted solution for correct input and over 5 times faster for incorrect input.

blocks|key|459634|text|最短的解决方案是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|459635|const+isCharDigit+=+n+=>+n+<+10;|code-block|syntax|javascript|459636|您还可以应用以下内容：|459637|const+isCharDigit+=+n+=>+Boolean(%2B%2Bn);

const+isCharDigit+=+n+=>+'/'+<+n+&&+n+<+':';

const+isCharDigit+=+n+=>+!!%2B%2Bn;|459638|如果要检查多个聊天字符，则可以使用next+variants|459639|正则表达式：|459640|const+isDigit+=+n+=>+/\d%2B/.test(n);|459641|比较：|459642|const+isDigit+=+n+=>+%2Bn+==+n;|459643|检查它是否不是NaN|459644|const+isDigit+=+n+=>+!isNaN(n);|459645|entityMap^0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|14|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|17|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|X|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

The shortest solution is: 

<pre><code>const isCharDigit = n =&gt; n &lt; 10;
</code></pre>

You can apply these as well:

<pre><code>const isCharDigit = n =&gt; Boolean(++n);

const isCharDigit = n =&gt; '/' &lt; n &amp;&amp; n &lt; ':';

const isCharDigit = n =&gt; !!++n;
</code></pre>

if you want to check more than 1 chatacter, you might use next variants

Regular Expression:

<pre><code>const isDigit = n =&gt; /\d+/.test(n);
</code></pre>

Comparison:

<pre><code>const isDigit = n =&gt; +n == n;
</code></pre>

Check if it is not NaN

<pre><code>const isDigit = n =&gt; !isNaN(n);
</code></pre>

blocks|key|673756|text|我建议使用简单的正则表达式。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673757|如果您只查找字符串中的最后一个字符：|673758|/%5E.*?[0-9]$/.test("blabla,120");++//+true
/%5E.*?[0-9]$/.test("blabla,120a");+//+false
/%5E.*?[0-9]$/.test("120");+++++++++//+true
/%5E.*?[0-9]$/.test(120);+++++++++++//+true
/%5E.*?[0-9]$/.test(undefined);+++++//+false
/%5E.*?[0-9]$/.test(-1);++++++++++++//+true
/%5E.*?[0-9]$/.test("-1");++++++++++//+true
/%5E.*?[0-9]$/.test(false);+++++++++//+false
/%5E.*?[0-9]$/.test(true);++++++++++//+false|code-block|syntax|javascript|673759|如果只检查一个字符作为输入，那么正则表达式就更简单了：|673760|var+char+=+"0";
/%5E[0-9]$/.test(char);+++++++++++++//+true|673761|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I suggest a simple regex.

If you're looking for just the last character in the string:

<pre><code>/^.*?[0-9]$/.test("blabla,120"); // true
/^.*?[0-9]$/.test("blabla,120a"); // false
/^.*?[0-9]$/.test("120"); // true
/^.*?[0-9]$/.test(120); // true
/^.*?[0-9]$/.test(undefined); // false
/^.*?[0-9]$/.test(-1); // true
/^.*?[0-9]$/.test("-1"); // true
/^.*?[0-9]$/.test(false); // false
/^.*?[0-9]$/.test(true); // false
</code></pre>

And the regex is even simpler if you are just checking a single char as an input:

<pre><code>var char = "0";
/^[0-9]$/.test(char); // true
</code></pre>

blocks|key|673254|text|如果要测试单个字符，则：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673255|var+isDigit+=+(function()+{
++++var+re+=+/%5E\d$/;
++++return+function(c)+{
++++++++return+re.test(c);
++++}
}());|code-block|syntax|javascript|673256|将返回true或false，这取决于c是否是数字。|673257|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 testing single characters, then:

<pre><code>var isDigit = (function() {
 var re = /^\d$/;
 return function(c) {
 return re.test(c);
 }
}());
</code></pre>

will return true or false depending on whether c is a digit or not.

blocks|key|459419|text|var+Is+=+{
++++character:+{
++++++++number:+(function()+{
++++++++++++//+Only+computed+once
++++++++++++var+zero+=+"0".charCodeAt(0),+nine+=+"9".charCodeAt(0);

++++++++++++return+function(c)+{
++++++++++++++++return+(c+=+c.charCodeAt(0))+>=+zero+&&+c+<=+nine;
++++++++++++}
++++++++})()
++++}
};|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|459420|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>var Is = {
 character: {
 number: (function() {
 // Only computed once
 var zero = "0".charCodeAt(0), nine = "9".charCodeAt(0);

 return function(c) {
 return (c = c.charCodeAt(0)) &gt;= zero &amp;&amp; c &lt;= nine;
 }
 })()
 }
};
</code></pre>

blocks|key|459387|text|isNumber+=+function(obj,+strict)+{
++++var+strict+=+strict+===+true+?+true+:+false;
++++if+(strict)+{
++++++++return+!isNaN(obj)+&&+obj+instanceof+Number+?+true+:+false;
++++}+else+{
++++++++return+!isNaN(obj+-+parseFloat(obj));
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|459388|不使用严格模式的输出：|unstyled|459389|var+num+=+14;
var+textnum+=+'14';
var+text+=+'yo';
var+nan+=+NaN;

isNumber(num);
isNumber(textnum);
isNumber(text);
isNumber(nan);

true
true
false
false|459390|严格模式下的输出：|459391|var+num+=+14;
var+textnum+=+'14';
var+text+=+'yo';
var+nan+=+NaN;

isNumber(num,+true);
isNumber(textnum,+true);
isNumber(text,+true);
isNumber(nan);

true
false
false
false|459392|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|M|3|-4|5|F|7|T|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>isNumber = function(obj, strict) {
 var strict = strict === true ? true : false;
 if (strict) {
 return !isNaN(obj) &amp;&amp; obj instanceof Number ? true : false;
 } else {
 return !isNaN(obj - parseFloat(obj));
 }
}
</code></pre>

output without strict mode:

<pre><code>var num = 14;
var textnum = '14';
var text = 'yo';
var nan = NaN;

isNumber(num);
isNumber(textnum);
isNumber(text);
isNumber(nan);

true
true
false
false
</code></pre>

output with strict mode:

<pre><code>var num = 14;
var textnum = '14';
var text = 'yo';
var nan = NaN;

isNumber(num, true);
isNumber(textnum, true);
isNumber(text, true);
isNumber(nan);

true
false
false
false
</code></pre>

blocks|key|673682|text|尝试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673683|function+is_numeric(str){
++++++++try+{
+++++++++++return+isFinite(str)
++++++++}
++++++++catch(err)+{
++++++++++++return+false
++++++++}
++++}|code-block|syntax|javascript|673684|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|$]]

Try:

<pre><code>function is_numeric(str){
 try {
 return isFinite(str)
 }
 catch(err) {
 return false
 }
 }
</code></pre>

blocks|key|459531|text|一个通过利用语言的动态类型检查的简单解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|459532|function+isNumber+(string)+{
+++//it+has+whitespace
+++if(string.trim()+===+''){
+++++return+false
+++}
+++return+string+-+0+===+string+*+1
}|code-block|syntax|javascript|459533|请参阅下面的测试用例|459534|​|459535|function+isNumber+(str)+{
+++if(str.trim()+===+''){
+++++return+false
+++}
+++return+str+-+0+===+str+*+1
}


console.log('-1'+%2B+'+→+'+%2B+isNumber+('-1'))++++
console.log('-1.5'+%2B+'+→+'+%2B+isNumber+('-1.5'))+
console.log('0'+%2B+'+→+'+%2B+isNumber+('0'))++++
console.log(',+,'+%2B+'+→+'+%2B+isNumber+(',+,'))++
console.log('0.42'+%2B+'+→+'+%2B+isNumber+('0.42'))+++
console.log('.42'+%2B+'+→+'+%2B+isNumber+('.42'))++++
console.log('#abcdef'+%2B+'+→+'+%2B+isNumber+('#abcdef'))
console.log('1.2.3'+%2B+'+→+'+%2B+isNumber+('1.2.3'))+
console.log(''+%2B+'+→+'+%2B+isNumber+(''))++++
console.log('blah'+%2B+'+→+'+%2B+isNumber+('blah'))|459536|459537|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Q|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|R|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|S|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|M|3|J|5|6|7|U|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|O|$]]

A simple solution by leveraging language's dynamic type checking:
<pre class="lang-js prettyprint-override"><code>function isNumber (string) {
 //it has whitespace
 if(string.trim() === ''){
 return false
 }
 return string - 0 === string * 1
}

</code></pre>
see test cases below
<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>function isNumber (str) {
 if(str.trim() === ''){
 return false
 }
 return str - 0 === str * 1
}


console.log('-1' + ' → ' + isNumber ('-1')) 
console.log('-1.5' + ' → ' + isNumber ('-1.5')) 
console.log('0' + ' → ' + isNumber ('0')) 
console.log(', ,' + ' → ' + isNumber (', ,')) 
console.log('0.42' + ' → ' + isNumber ('0.42')) 
console.log('.42' + ' → ' + isNumber ('.42')) 
console.log('#abcdef' + ' → ' + isNumber ('#abcdef'))
console.log('1.2.3' + ' → ' + isNumber ('1.2.3')) 
console.log('' + ' → ' + isNumber ('')) 
console.log('blah' + ' → ' + isNumber ('blah'))</code></pre>
</div>
</div>

blocks|key|673990|text|组合使用isNaN和parseInt函数：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|673991|var+character+=+...+;+//+your+character
var+isDigit+=+!+isNaN(+parseInt(character)+);|code-block|syntax|javascript|673992|另一种值得注意的方法-乘以1(如character+*+1而不是parseInt(character))+-不仅可以从任何数字字符串中生成数字，还可以从空字符串和只包含空格的字符串中生成0，因此它不适用于这里。|673993|entityMap^0|4|5|A|8|0|0|G|D|W|J|2L|1|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|N|$]]

Use combination of <code>isNaN</code> and <code>parseInt</code> functions:
<pre class="lang-js prettyprint-override"><code>var character = ... ; // your character
var isDigit = ! isNaN( parseInt(character) );
</code></pre>
Another notable way - multiplication by one (like <code>character * 1</code> instead of <code>parseInt(character)</code>) - makes a number not only from any numeric string, but also a <code>0</code> from empty string and a string containing only spaces so it is not suitable here.

blocks|key|459723|text|与上面的答案类似，我使用了|type|unstyled|depth|inlineStyleRanges|entityRanges|data|459724|+var+sum+=+0;+//some+value
+let+num+=+parseInt(val);+//or+just+Number.parseInt
+if(!isNaN(num))+{
+++++sum+%2B=+num;
+}|code-block|syntax|javascript|459725|这篇博文提供了更多关于这个check+if+a+string+is+numeric+in+Javascript+%7C+Typescript+&+ES6+的信息|offset|length|459726|entityMap|0|LINK|mutability|MUTABLE|url|https://mydaytodo.com/check-string-is-numeric-javascript-typescript/^0|0|0|D|1Q|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]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Similar to one of the answers above, I used

<pre><code> var sum = 0; //some value
 let num = parseInt(val); //or just Number.parseInt
 if(!isNaN(num)) {
 sum += num;
 }
</code></pre>

This blogpost sheds some more light on this <a href="https://mydaytodo.com/check-string-is-numeric-javascript-typescript/" rel="nofollow noreferrer">check if a string is numeric in Javascript | Typescript &amp; ES6 </a>

blocks|key|673266|text|function+is_numeric(mixed_var)+{
++++return+(typeof(mixed_var)+===+'number'+%7C%7C+typeof(mixed_var)+===+'string')+&&
++++++++mixed_var+!==+''+&&+!isNaN(mixed_var);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|673267|Source+code|unstyled|offset|length|673268|entityMap|0|LINK|mutability|MUTABLE|url|http://phpjs.org/functions/is_numeric/^0|0|0|B|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>function is_numeric(mixed_var) {
 return (typeof(mixed_var) === 'number' || typeof(mixed_var) === 'string') &amp;&amp;
 mixed_var !== '' &amp;&amp; !isNaN(mixed_var);
}
</code></pre>

<a href="http://phpjs.org/functions/is_numeric/" rel="nofollow noreferrer">Source code</a>

blocks|key|459199|text|square+=+function(a)+{
++++if+((a+*+0)+==+0)+{
++++++++return+a*a;
++++}+else+{
++++++++return+"Enter+a+valid+number.";
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|459200|Source|unstyled|offset|length|459201|entityMap|0|LINK|mutability|MUTABLE|url|http://jacksondunstan.com/articles/983^0|0|0|6|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>square = function(a) {
 if ((a * 0) == 0) {
 return a*a;
 } else {
 return "Enter a valid number.";
 }
}
</code></pre>

<a href="http://jacksondunstan.com/articles/983" rel="nofollow noreferrer">Source</a>

blocks|key|673487|text|你可以试试这个(在我的例子中是有效的)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|673488|如果要测试字符串的第一个字符是否为int：|673489|if+(parseInt(YOUR_STRING.slice(0,+1)))+{
++++alert("first+char+is+int")
}+else+{
++++alert("first+char+is+not+int")
}|code-block|syntax|javascript|673490|如果您想测试char是否为int类型：|673491|if+(parseInt(YOUR_CHAR))+{
++++alert("first+char+is+int")
}+else+{
++++alert("first+char+is+not+int")
}|673492|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

You can try this (worked in my case)

If you want to test if the first char of a string is an int:

<pre><code>if (parseInt(YOUR_STRING.slice(0, 1))) {
 alert("first char is int")
} else {
 alert("first char is not int")
}
</code></pre>

If you want to test if the char is a int:

<pre><code>if (parseInt(YOUR_CHAR)) {
 alert("first char is int")
} else {
 alert("first char is not int")
}
</code></pre>

blocks|key|459597|text|这个函数适用于我能找到的所有测试用例。它的速度也比：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|459598|function+isNumeric+(n)+{
++if+(!isNaN(parseFloat(n))+&&+isFinite(n)+&&+!hasLeading0s(n))+{
++++return+true;
++}
++var+_n+=+%2Bn;
++return+_n+===+Infinity+%7C%7C+_n+===+-Infinity;
}|code-block|syntax|javascript|459599|​|459600|var+isIntegerTest+=+/%5E\d%2B$/;
var+isDigitArray+=+[!0,+!0,+!0,+!0,+!0,+!0,+!0,+!0,+!0,+!0];

function+hasLeading0s(s)+{
++return+!(typeof+s+!==+'string'+%7C%7C
++++s.length+<+2+%7C%7C
++++s[0]+!==+'0'+%7C%7C
++++!isDigitArray[s[1]]+%7C%7C
++++isIntegerTest.test(s));
}
var+isWhiteSpaceTest+=+/\s/;

function+fIsNaN(n)+{
++return+!(n+<=+0)+&&+!(n+>+0);
}

function+isNumber(s)+{
++var+t+=+typeof+s;
++if+(t+===+'number')+{
++++return+(s+<=+0)+%7C%7C+(s+>+0);
++}+else+if+(t+===+'string')+{
++++var+n+=+%2Bs;
++++return+!(fIsNaN(n)+%7C%7C+hasLeading0s(s)+%7C%7C+!(n+!==+0+%7C%7C+!(s+===+''+%7C%7C+isWhiteSpaceTest.test(s))));
++}+else+if+(t+===+'object')+{
++++return+!(!(s+instanceof+Number)+%7C%7C+fIsNaN(%2Bs));
++}
++return+false;
}

function+testRunner(IsNumeric)+{
++var+total+=+0;
++var+passed+=+0;
++var+failedTests+=+[];

++function+test(value,+result)+{
++++total%2B%2B;
++++if+(IsNumeric(value)+===+result)+{
++++++passed%2B%2B;
++++}+else+{
++++++failedTests.push({
++++++++value:+value,
++++++++expected:+result
++++++});
++++}
++}
++//+true
++test(0,+true);
++test(1,+true);
++test(-1,+true);
++test(Infinity,+true);
++test('Infinity',+true);
++test(-Infinity,+true);
++test('-Infinity',+true);
++test(1.1,+true);
++test(-0.12e-34,+true);
++test(8e5,+true);
++test('1',+true);
++test('0',+true);
++test('-1',+true);
++test('1.1',+true);
++test('11.112',+true);
++test('.1',+true);
++test('.12e34',+true);
++test('-.12e34',+true);
++test('.12e-34',+true);
++test('-.12e-34',+true);
++test('8e5',+true);
++test('0x89f',+true);
++test('00',+true);
++test('01',+true);
++test('10',+true);
++test('0e1',+true);
++test('0e01',+true);
++test('.0',+true);
++test('0.',+true);
++test('.0e1',+true);
++test('0.e1',+true);
++test('0.e00',+true);
++test('0xf',+true);
++test('0Xf',+true);
++test(Date.now(),+true);
++test(new+Number(0),+true);
++test(new+Number(1e3),+true);
++test(new+Number(0.1234),+true);
++test(new+Number(Infinity),+true);
++test(new+Number(-Infinity),+true);
++//+false
++test('',+false);
++test('+',+false);
++test(false,+false);
++test('false',+false);
++test(true,+false);
++test('true',+false);
++test('99,999',+false);
++test('#abcdef',+false);
++test('1.2.3',+false);
++test('blah',+false);
++test('\t\t',+false);
++test('\n\r',+false);
++test('\r',+false);
++test(NaN,+false);
++test('NaN',+false);
++test(null,+false);
++test('null',+false);
++test(new+Date(),+false);
++test({},+false);
++test([],+false);
++test(new+Int8Array(),+false);
++test(new+Uint8Array(),+false);
++test(new+Uint8ClampedArray(),+false);
++test(new+Int16Array(),+false);
++test(new+Uint16Array(),+false);
++test(new+Int32Array(),+false);
++test(new+Uint32Array(),+false);
++test(new+BigInt64Array(),+false);
++test(new+BigUint64Array(),+false);
++test(new+Float32Array(),+false);
++test(new+Float64Array(),+false);
++test('.e0',+false);
++test('.',+false);
++test('00e1',+false);
++test('01e1',+false);
++test('00.0',+false);
++test('01.05',+false);
++test('00x0',+false);
++test(new+Number(NaN),+false);
++test(new+Number('abc'),+false);
++console.log('Passed+'+%2B+passed+%2B+'+of+'+%2B+total+%2B+'+tests.');
++if+(failedTests.length+>+0)+console.log({
++++failedTests:+failedTests
++});
}
testRunner(isNumber)|459601|459602|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|O|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|P|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Q|8|@]|9|@]|A|$E|F]]|$1|K|3|H|5|6|7|R|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|M|$]]

This function works for all test cases that i could find.
It's also faster than:

<pre><code>function isNumeric (n) {
 if (!isNaN(parseFloat(n)) &amp;&amp; isFinite(n) &amp;&amp; !hasLeading0s(n)) {
 return true;
 }
 var _n = +n;
 return _n === Infinity || _n === -Infinity;
}
</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>var isIntegerTest = /^\d+$/;
var isDigitArray = [!0, !0, !0, !0, !0, !0, !0, !0, !0, !0];

function hasLeading0s(s) {
 return !(typeof s !== 'string' ||
 s.length &lt; 2 ||
 s[0] !== '0' ||
 !isDigitArray[s[1]] ||
 isIntegerTest.test(s));
}
var isWhiteSpaceTest = /\s/;

function fIsNaN(n) {
 return !(n &lt;= 0) &amp;&amp; !(n &gt; 0);
}

function isNumber(s) {
 var t = typeof s;
 if (t === 'number') {
 return (s &lt;= 0) || (s &gt; 0);
 } else if (t === 'string') {
 var n = +s;
 return !(fIsNaN(n) || hasLeading0s(s) || !(n !== 0 || !(s === '' || isWhiteSpaceTest.test(s))));
 } else if (t === 'object') {
 return !(!(s instanceof Number) || fIsNaN(+s));
 }
 return false;
}

function testRunner(IsNumeric) {
 var total = 0;
 var passed = 0;
 var failedTests = [];

 function test(value, result) {
 total++;
 if (IsNumeric(value) === result) {
 passed++;
 } else {
 failedTests.push({
 value: value,
 expected: result
 });
 }
 }
 // true
 test(0, true);
 test(1, true);
 test(-1, true);
 test(Infinity, true);
 test('Infinity', true);
 test(-Infinity, true);
 test('-Infinity', true);
 test(1.1, true);
 test(-0.12e-34, true);
 test(8e5, true);
 test('1', true);
 test('0', true);
 test('-1', true);
 test('1.1', true);
 test('11.112', true);
 test('.1', true);
 test('.12e34', true);
 test('-.12e34', true);
 test('.12e-34', true);
 test('-.12e-34', true);
 test('8e5', true);
 test('0x89f', true);
 test('00', true);
 test('01', true);
 test('10', true);
 test('0e1', true);
 test('0e01', true);
 test('.0', true);
 test('0.', true);
 test('.0e1', true);
 test('0.e1', true);
 test('0.e00', true);
 test('0xf', true);
 test('0Xf', true);
 test(Date.now(), true);
 test(new Number(0), true);
 test(new Number(1e3), true);
 test(new Number(0.1234), true);
 test(new Number(Infinity), true);
 test(new Number(-Infinity), true);
 // false
 test('', false);
 test(' ', false);
 test(false, false);
 test('false', false);
 test(true, false);
 test('true', false);
 test('99,999', false);
 test('#abcdef', false);
 test('1.2.3', false);
 test('blah', false);
 test('\t\t', false);
 test('\n\r', false);
 test('\r', false);
 test(NaN, false);
 test('NaN', false);
 test(null, false);
 test('null', false);
 test(new Date(), false);
 test({}, false);
 test([], false);
 test(new Int8Array(), false);
 test(new Uint8Array(), false);
 test(new Uint8ClampedArray(), false);
 test(new Int16Array(), false);
 test(new Uint16Array(), false);
 test(new Int32Array(), false);
 test(new Uint32Array(), false);
 test(new BigInt64Array(), false);
 test(new BigUint64Array(), false);
 test(new Float32Array(), false);
 test(new Float64Array(), false);
 test('.e0', false);
 test('.', false);
 test('00e1', false);
 test('01e1', false);
 test('00.0', false);
 test('01.05', false);
 test('00x0', false);
 test(new Number(NaN), false);
 test(new Number('abc'), false);
 console.log('Passed ' + passed + ' of ' + total + ' tests.');
 if (failedTests.length &gt; 0) console.log({
 failedTests: failedTests
 });
}
testRunner(isNumber)</code></pre>
</div>
</div>

blocks|key|674032|text|下面是一个执行此操作的简单函数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|674033|function+is_number(char)+{{
++++return+!isNaN(parseInt(char));
}}

Returns:++true,+false|code-block|syntax|javascript|674034|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|$]]

Here is a simple function that does it.
<pre><code>function is_number(char) {{
 return !isNaN(parseInt(char));
}}

Returns: true, false
</code></pre>

blocks|key|674049|text|我使用的是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|674050|const+isNumber+=+(str)+=>+(
++++str.length+===+str.trim().length+
++++&&+str.length+>+0
++++&&+Number(str)+>=+0
)|code-block|syntax|javascript|674051|它适用于字符串或单个字符。|674052|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 am using this:
<pre><code>const isNumber = (str) =&gt; (
 str.length === str.trim().length 
 &amp;&amp; str.length &gt; 0
 &amp;&amp; Number(str) &gt;= 0
)
</code></pre>
It works for strings or single characters.

blocks|key|674102|text|将此answer修改为更方便，并限制为字符(而不是字符串)：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|674103|const+charCodeZero+=+"0".charCodeAt(0);
const+charCodeNine+=+"9".charCodeAt(0);
function+isDigit(s:string)+{
++++return+s.length==1&&+s.charCodeAt(0)+>=+charCodeZero+&&+s.charCodeAt(0)+<=+charCodeNine;
}

console.log(isDigit('4'))+++//true
console.log(isDigit('4s'))++//false
console.log(isDigit('s'))+++//false|code-block|syntax|javascript|674104|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/38370808/10577976^0|2|6|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]]]]

modifying this <a href="https://stackoverflow.com/a/38370808/10577976">answer</a> to be little more convenient and limiting to chars(and not string):
<pre class="lang-js prettyprint-override"><code>const charCodeZero = &quot;0&quot;.charCodeAt(0);
const charCodeNine = &quot;9&quot;.charCodeAt(0);
function isDigit(s:string) {
 return s.length==1&amp;&amp; s.charCodeAt(0) &gt;= charCodeZero &amp;&amp; s.charCodeAt(0) &lt;= charCodeNine;
}

console.log(isDigit('4')) //true
console.log(isDigit('4s')) //false
console.log(isDigit('s')) //false

</code></pre>

blocks|key|673670|text|只需使用isFinite即可|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|673671|const+number+=+"1";
if+(isFinite(number))+{
++++//+do+something
}|code-block|syntax|javascript|673672|entityMap^0|4|8|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|$]]

Just use <code>isFinite</code>

<pre><code>const number = "1";
if (isFinite(number)) {
 // do something
}
</code></pre>

I need to check whether <code>justPrices[i].substr(commapos+2,1)</code>.

The string is something like: "blabla,120"

In this case it would check whether '0' is a number. How can this be done?

Check if character is number?

我需要检查一下justPrices[i].substr(commapos+2,1)是否。字符串类似于："blabla,120“在这种情况下，它将检查'0‘是否是一个数字。如何做到这一点？

问是否检查字符是否为数字？
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回答 22

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问是否检查字符是否为数字？EN

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问是否检查字符是否为数字？
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