Samples a given number of characters from a given string

sample.js

// sample.js
// Samples a given number of characters from a given string.
// Example;
//     sample('0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz', 4); // Eg. 'uY7m'
function sample(characters, length) {
    var result = '';
    for (var i = 0; i < length; i++) {
        result += getRandomChar(characters);
    }
    return result;
}

function getRandomChar(characters) {
    return characters[getRandomInteger(characters.length)];
}

function getRandomInteger(max) {
    return Math.floor(Math.random() * max);
}