Generate random string/characters in JavaScript

Question

I want a 5 character string composed of characters picked randomly from the set [a-zA-Z0-9].

What's the best way to do this with JavaScript?

Answer 1

I think this will work for you:

function makeid(length) {
    var result           = '';
    var characters       = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    var charactersLength = characters.length;
    for ( var i = 0; i < length; i++ ) {
      result += characters.charAt(Math.floor(Math.random() * 
 charactersLength));
   }
   return result;
}

console.log(makeid(5));

Answer 2

//Can change 7 to 2 for longer results.
let r = (Math.random() + 1).toString(36).substring(7);
console.log("random", r);

Note: The above algorithm has the following weaknesses:

• It will generate anywhere between 0 and 6 characters due to the fact that trailing zeros get removed when stringifying floating points.
• It depends deeply on the algorithm used to stringify floating point numbers, which is horrifically complex. (See the paper "How to Print Floating-Point Numbers Accurately".)
• Math.random() may produce predictable ("random-looking" but not really random) output depending on the implementation. The resulting string is not suitable when you need to guarantee uniqueness or unpredictability.
• Even if it produced 6 uniformly random, unpredictable characters, you can expect to see a duplicate after generating only about 50,000 strings, due to the birthday paradox. (sqrt(36^6) = 46656)