js change random letter in a string code example

Example 1: javascript get random string

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

//usage: getRandomString(20); // pass desired length of random string

Example 2: random string js

const string_length = 10
[...Array(string_length)].map(i=>(~~(Math.random()*36)).toString(36)).join('')