Shortest code to get random string of numbers and letters

Question

I use Math.random() right now, it returns some number like 0.7183306051883847. There're some bad sides of this function:

0. at the beginning
no option to set a symbols length of the number
no option to add letters to the string

I wonder, what is the shortest code to generate strings like (expected characters length - 6 for example)?

2en81u
39438s
ldksfn

Thanks.

I am sorry, were you looking for http://codegolf.stackexchange.com? — thefourtheye, Dec 22 '13 at 11:17
@Steve: "What do you want" and "What have you tried" are not the same thing — Eric, Dec 22 '13 at 11:25

score 10 · Accepted Answer · 2014-03-13T09:42:58.787

10

This should be the shortest. If you need it uppercased, add an extra .toUpperCase() call at the tail.

Math.random().toString(36).substring(3,9)

Updated

This version is a bit longer, but it does avoid the problem that some special rational number may not have enough length.

(+new Date * Math.random()).toString(36).substring(0,6)

edited Mar 13 '14 at 09:42

answered Dec 22 '13 at 11:27

2

http://stackoverflow.com/a/8084248/3110638 – Jonny 5 Dec 22 '13 at 11:31
@Jonny5 Aha. It seems that this is a widely used skill for generating random passwords extremely quickly. – Dec 22 '13 at 11:38
Well, was the first, that google found :-) gertas comment from the linked thread might be integrated in this solution. – Jonny 5 Dec 22 '13 at 11:41
1

This can't possibly work in all cases. Math.random() can return any float value in the range, including values like 0.5, 0.25, and so on, that don't have enough digits when stringified. toString() will not add the extra 0s for you. The right thing to do is use the value itself--not the string representation of it--appropriately scaled and rounded, to index an array of characters. – Lee Daniel Crocker Dec 22 '13 at 17:34
@LeeDanielCrocker I got a new idea by multiplying a big interger (timestamp). – Mar 13 '14 at 09:43

score 2 · Answer 2 · answered Dec 22 '13 at 11:26

2

btoa does the job, but not particularly well:

> btoa(Math.random())
"MC43MzU0MzQ4NTk5OTEwNzM2"
> btoa(Math.random())
"MC44MTk2NzE0OTIzMjUxNDI="
> btoa(Math.random())
"MC41NDgwMzgxMzMxODcyMTk1"
> btoa(Math.random())
"MC4wNTk4NDc1NDIzMTc1ODQxNg=="
> btoa(Math.random())
"MC41NjA1NzYxNTEzNTc5NjM3"
> btoa(Math.random())
"MC4xMTA5MzY5ODY5ODA5NTk3Nw=="
> btoa(Math.random())
"MC42NDgwNzM5NjY2MTQ5MDI="
> btoa(Math.random())
"MC4zMTkzNTM2OTQzMjkwMzgyNg=="
> btoa(Math.random())
"MC4yOTU2OTgyOTE4NTQ5MzI5"
> btoa(Math.random())
"MC44ODc3MDEzNjQ0NjY5MjA1"

Note how they all start with MC4, since Math.random().toString() always starts with 0.

answered Dec 22 '13 at 11:26

Eric

95,302
53
242
374

There're unwanted `==` at the end and uppercased letters. – Jasper Dec 22 '13 at 11:30
@steve: `.toLower().replace(/=/g, '')` – Eric Dec 22 '13 at 11:33
Also, btoa isn't supported by ie9, only ie10+ – Jasper Dec 22 '13 at 11:34

Azadeh Radkianpour · Answer 3 · 2013-12-22T11:39:33.767

2

function randomString() {
    var chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz";
    var string_length = 8;
    var randomstring = '';
    for (var i = 0; i < string_length; i++) {
        var rnum = Math.floor(Math.random() * chars.length);
        randomstring += chars[rnum];
    }
    return randomstring;
}

edited Dec 22 '13 at 11:39

answered Dec 22 '13 at 11:29

Azadeh Radkianpour

961
9
18

1

`chars.substring(rnum, rnum + 1)` => `chars[rnum]` – Eric Dec 22 '13 at 11:31
thanks, but this function is too long. – Jasper Dec 22 '13 at 11:31
1

@Steve: Please, explain how a piece of code can be "too long"? – Eric Dec 22 '13 at 11:32
1

I don't understand. where does 'the shortest code logic' come from? This is a good function and the chance of returning duplicate word is very low. – Azadeh Radkianpour Dec 22 '13 at 11:36
@Jasper code golf is off topic for this site. – Tim Seguine Jan 16 '14 at 21:55
1

Regarding, the accepted answer will be much longer when you need let's say 60 char long strings, and this still fits, I gave my vote for this answer. – René Baudisch Feb 26 '21 at 14:37

bgusach · Answer 4 · 2013-12-22T11:32:46.920

0

Get an array of ints that will be translated to your random string, something like this:

var myAscii = [],
    someAscii;
for (var i = 0; i < 5; i +=1) {
    someAscii = Math.floor(Math.random() * (90 - 65)) + 65; // This gives you a random number between 65 and 90, which is the upper case A-Z. Adapt it to your stuff.
    myAscii.push(someAscii);
}
var randomString = String.fromCharCode.apply(someAscii);

Anyway, it is a simpler approach to get a string with all the desired characters and perform a random extraction, as the related answer proposes.

edited Dec 22 '13 at 11:32

answered Dec 22 '13 at 11:18

bgusach

14,527
14
51
68

Never name your variables as `char` – thefourtheye Dec 22 '13 at 11:18
Actually, I don't need maxNumber option, I need maxSymbols option instead – Jasper Dec 22 '13 at 11:21
@thefourtheye: Why not? – Eric Dec 22 '13 at 11:22
fromCharCode is nothing, since it doesn't give a random string with an expected length of symbols – Jasper Dec 22 '13 at 11:22
Doesn't work. Why are you passing for var someAscii last value to String.fromCharCode? – René Baudisch Feb 26 '21 at 14:28

Shortest code to get random string of numbers and letters

4 Answers4