Numbers, Hex, and Colors

Justin just made a post to his blog showing a nifty solution for converting an 8-bit number into a hex string, that’s now built into Prototype.

I took the code, fleshed it out, and made a complementary function (converting from hex to a number). Here they are for you to enjoy:

// JS Hex/Number: Copyright 2007, John Resig
function toHex(){
  var ret = "";
  for ( var i = 0; i < arguments.length; i++ )
    ret += (arguments&#91;i&#93; < 16 ? "0" : "") + arguments&#91;i&#93;.toString(16);
  return ret.toUpperCase();

function toNumbers( str ){
  var ret = &#91;&#93;;
   str.replace(/(..)/g, function(str){
    ret.push( parseInt( str, 16 ) );
  return ret;

And then they can be used like so:
&#91;js&#93;toHex( 125, 255, 0 )
>> "7DFF00"
toNumbers( "7DFF00" )
>> [ 125, 255, 0 ]

I love using the “secret” extra argument to parseInt – allowing to specify the base of the number that you’re parsing. You simply up it to 16 and you now have a dead-simple hex-to-number convertor.

If we had JavaScript 1.6 today we’d be able to use to make some of the above less painful, like so:

return arguments, function(num){
  return (num < 16 ? "0" : "") + num.toString(16);

and be able to have fun with the array comprehension of <a href="">JavaScript 1.7</a>:
[js]function range(end) {
  for (let i = 0; i < end; i++)
    yield i;
&#91; i.toString(16) for ( i in range(16) ) &#93;&#91; num & 0x0F &#93;&#91;/js&#93;

<b>Update:</b> So you can specify the base of a number in the number's .toString(). Huh, you learn something new everyday! In retrospect, I don't know why I was doing the array comprehension at all when I could've just done this:


Side Note: It really irks me that there’s no built-in “range” utility for array comprehension. Maybe if the comprehension wasn’t limited to just loops, and it included normal for loops, instead? Oh well, water under the bridge at this point.

Posted: May 2nd, 2007

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