Generate and copy to clipboard strong password - Tampermonkey script

generatePassword.js

// ==UserScript==
// @name         Generate Strong Password
// @namespace    http://tampermonkey.net/
// @version      3.1.1
// @description  Strong password generator of size 12
// @author       Piyush Singh
// @match        *://*/*
// @icon         data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==
// @grant        unsafeWindow
// @grant        GM_setClipboard
// ==/UserScript==

// To Use just press Ctrl+G and you will have a strong password in your clipboard.
// Can also be used from your browser console by `genpwd()`


// Fisher Yates algorithm to shuffle an array and return first n elements
function fisherYates(arr, n)
{
	var i = arr.length;
	while (i--)
	{
		var idx = Math.floor(i * Math.random());
		[arr[i],arr[idx]] = [arr[idx],arr[i]];
	}
	return arr.slice(0,n);
}


function genpwd()
{
    var lowercase = "abcdefghijlmnopqrstuvwxyz";
    var uppercase = "ABCDEFGHIJLMNOPQRSTUVWXYZ";
    var digits = "0123456789";
    var punctuation = "#$%()*./:<=>?@|~";

    var low = fisherYates(lowercase.split(''),3);
    var upp = fisherYates(uppercase.split(''),3);
    var dig = fisherYates(digits.split(''),3);
    var pun = fisherYates(punctuation.split(''),3);

    var pwd = [].concat(low,upp,dig,pun);
    pwd = fisherYates(pwd,12);
    var password = pwd.join('')
    return password;
}



(function() {
    'use strict';
    if(!unsafeWindow.genpwd) unsafeWindow.genpwd = genpwd;

    document.onkeyup=function(ev){
        // var ev = ev || window.event; // for IE to cover IEs window object
        if(ev.ctrlKey && ev.which == 71) {
            var password = genpwd();
            GM_setClipboard(password);
            return false;
        }
    }

})();