GENERATE PASSWORD

js:

var letters = ['a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'];

var letterb = ['A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];

var numbers = ['0','1','2','3','4','5','6','7','8','9'];

var pass = "";
window.onload = function(){
	pass = document.getElementById('pass');	
}

function getWord(length,useBig,useSmall,useNumbers){
  var words="";
  words = useBig ? useSmall ? useNumbers ? letterb.concat(letters).concat(numbers) : letterb.concat(letters) : useNumbers ? letterb.concat(numbers) : letterb : useSmall ? useNumbers ? letters.concat(numbers) : letters : useNumbers ? numbers : "";
  var word = "";
  if(words!==""){
    for(var i=0; i < length; i++){
      var random = Math.floor(Math.random()*(words.length));
      word += words[random];
    }
  }
  return word;
}

function getElementByName(name,tagName){
  var tag = "";
  if(tagName) tag = document.getElementsByTagName(tagName);
  else tag = document.getElementsByTagName('input');
  for(var i=0, len = tag.length; i < len; i++){
    if(tag[i].name == name) return tag[i];
  }
  return;
}

function generate(){
  var len = getElementByName('length');
  if(!len.value || !(parseFloat(len.value))){
    alert('Length must be a number');
    return;
  }
  len = parseFloat(len.value);
  var word = "";
  var big = getElementByName('letterb');
  var small = getElementByName('letters');
  var nums = getElementByName('numbers');
  word = getWord(len,big.checked,small.checked,nums.checked);
  pass.innerHTML = word;
}

html:

<form method="post" action="javascript:void(0)">
    <input type="text" size="6" name="length" value="Length" /><br />
    <input type="checkbox" name="letterb" /> Big letters ?<br />
    <input type="checkbox" name="letters" /> Small letters ?<br />
    <input type="checkbox" name="numbers" /> Numbers<br />
    <input type="submit" name="submit" onclick="return generate();" value="Generate Password" />
  </form>
  
  <p id="pass"></p>