How to generate a random string of letters and numbers in Javascript?

Question

I have been using this code:

function stringGen()
{
    var text = " ";

    var charset = "abcdefghijklmnopqrstuvwxyz0123456789";

    for( var i=0; i < len; i++ )
        text += charset.charAt(Math.floor(Math.random() * charset.length));

    return text;
}

But so far, it has not been working, like at all. What am I doing wrong?

Thank you for your help in advance

If you are using `Lodash` or `Underscore`, then http://stackoverflow.com/questions/1349404/generate-a-string-of-5-random-characters-in-javascript/36734713#36734713 — vineet, Apr 20 '16 at 05:44

Antony · Answer 1 · 2018-04-29T01:47:52.813

31

You missed the parameter len.

function stringGen(len) {
  var text = "";
  
  var charset = "abcdefghijklmnopqrstuvwxyz0123456789";
  
  for (var i = 0; i < len; i++)
    text += charset.charAt(Math.floor(Math.random() * charset.length));
  
  return text;
}

console.log(stringGen(3));

This would give you something like "a1z".

edited Apr 29 '18 at 01:47

answered Apr 19 '13 at 14:16

Antony

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+1 This one looks more correct than mine as it allows you to define the length of the string you need. – techfoobar Apr 19 '13 at 14:17

robahl · Answer 2 · 2014-04-23T19:03:43.857

10

A pretty one-liner would be:

Math.random().toString(36).substr(2, length)

Or if you need a str that is longer than 10/11 characters:

function generateRandAlphaNumStr(len) {
  var rdmString = "";
  for( ; rdmString.length < len; rdmString  += Math.random().toString(36).substr(2));
  return  rdmString.substr(0, len);

}

edited Apr 23 '14 at 19:03

answered Apr 21 '14 at 12:21

robahl

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The maximum `length` is `11` and, depending on the random number generated, sometimes you get `10` characters instead. – Tom Fenech Apr 21 '14 at 13:16
Yea that's true, good point :) – robahl Apr 21 '14 at 13:43
Now fixed for "unlimited" length. – robahl Apr 23 '14 at 19:04
If conciseness was your aim, you could put the `var rdmString = ""` into the first part of the `for` loop – Tom Fenech Apr 23 '14 at 19:06
Instead of substring, you can better use "slice()". For eg, `Math.random().toString(34).slice(2);` – Abdul Vajid Mar 17 '16 at 11:40

score 2 · Answer 3 · answered Apr 19 '13 at 14:22

2

Just as alternative:

var len = 20,
    str = '';

while( len-- ) {
    str += String.fromCharCode( 48 + ~~(Math.random() * 42) );
}

console.log( str );

answered Apr 19 '13 at 14:22

jAndy

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This is more than alphanumeric. Anyway the OP must have copied the function somewhere. – Antony Apr 19 '13 at 14:24
@Antony true, I was a little lazy. To get pure alpha nummericals we would need to limit the ascii range more. However, I felt like this is a more generic approach as having a pre-defined map of characters. – jAndy Apr 19 '13 at 14:27

score 1 · Answer 4 · answered Apr 19 '13 at 14:17

Your len variable is undefined. Either pass it in as a parameter, or set it to something.

function stringGen(len)
{
    var text = " ";

    var charset = "abcdefghijklmnopqrstuvwxyz0123456789";

    for( var i=0; i < len; i++ )
        text += charset.charAt(Math.floor(Math.random() * charset.length));

    return text;
}
alert(stringGen(5));

http://jsfiddle.net/rg7Z3/

How to generate a random string of letters and numbers in Javascript?

4 Answers4

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