Best way to alphanumeric check in JavaScript

You can use this regex /^[a-z0-9]+$/i

The asker's original inclination to use str.charCodeAt(i) appears to be faster than the regular expression alternative. In my test on jsPerf the RegExp option performs 66% slower in Chrome 36 (and slightly slower in Firefox 31).

Here's a cleaned-up version of the original validation code that receives a string and returns true or false:

function isAlphaNumeric(str) {
  var code, i, len;

  for (i = 0, len = str.length; i < len; i++) {
    code = str.charCodeAt(i);
    if (!(code > 47 && code < 58) && // numeric (0-9)
        !(code > 64 && code < 91) && // upper alpha (A-Z)
        !(code > 96 && code < 123)) { // lower alpha (a-z)
      return false;
    }
  }
  return true;
};

Of course, there may be other considerations, such as readability. A one-line regular expression is definitely prettier to look at. But if you're strictly concerned with speed, you may want to consider this alternative.

Check it with a regex.

Javascript regexen don't have POSIX character classes, so you have to write character ranges manually:

if (!input_string.match(/^[0-9a-z]+$/))
  show_error_or_something()

Here ^ means beginning of string and $ means end of string, and [0-9a-z]+ means one or more of character from 0 to 9 OR from a to z.

More information on Javascript regexen here: https://developer.mozilla.org/en/JavaScript/Guide/Regular_Expressions

You don't need to do it one at a time. Just do a test for any that are not alpha-numeric. If one is found, the validation fails.

function validateCode(){
    var TCode = document.getElementById('TCode').value;
    if( /[^a-zA-Z0-9]/.test( TCode ) ) {
       alert('Input is not alphanumeric');
       return false;
    }
    return true;     
 }

If there's at least one match of a non alpha numeric, it will return false.

To match all Unicode letters and numbers you can use a Unicode regex:

const alphanumeric = /^[\p{L}\p{N}]*$/u;

const valid   = "Jòhn꠵Çoe日本語3rd"; // <- these are all letters or numbers
const invalid = "JohnDoe3rd!";

console.log(valid.match(alphanumeric));
console.log(invalid.match(alphanumeric));

In the above regex the u flag enables Unicode mode. \p{L} is short for \p{Letter} and \p{N} is short for \p{Number}. The square brackets [] surrounding them is a normal character class, meaning that a character must be either a letter or a number (in this context). The * is "zero or more", you can change this into + (one or more) if you don't want to allow empty strings .^/$ matches the start/end of the string.

The above will suffice most cases, but might match more than you want. You might not want to match Latin, Arabic, Cyrillic, etc. You might only want to match Latin letters and decimal numbers.

const alphanumeric = /^[\p{sc=Latn}\p{Nd}]*$/u;

const valid   = "JòhnÇoe3rd";
const invalid = "Jòhn꠵Çoe日本語3rd";

console.log(valid.match(alphanumeric));
console.log(invalid.match(alphanumeric));

\p{sc=Latn} is short for \p{Script=Latin}. \p{Nd} is short for \p{Decimal_Number} and matches decimals. The difference with \d is that \p{Nd} does not only match 5, but also 𝟓, ５ and possibly more.

Checkout the regex Unicode documentation for details, available \p options are linked on the documentation page.

Note that the u flag is not supported by Internet Explorer.

Best way to alphanumeric check in JavaScript

Related

Recent Posts