JavaScript Generate Random String

random_string.js

// get random string by length `len`
function _getRandomString(len) {
    len = len || 32;
    var $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYAabcdefghijklmnopqrstuvwxyz0123456789_'; // string set
    var maxPos = $chars.length;
    var pwd = '';
    for (i = 0; i < len; i++) {
        pwd += $chars.charAt(Math.floor(Math.random() * maxPos));
    }
    return pwd;
}