Transform string in JavaScript

How would you do this...?

I am trying to write a string transformer, which capitalises certain letter in string.

Examples

lorem lipum lampum => lorem Lipum lampum
po开发者_如何学Gopud pidem papusek => popud pidem Papusek

Thanks!

This should randomly capitalize every fifth string:

var s = "lorem lipum lampum";
var a = s.split(" ");
for (var i=0; i < a.length; i++) {
 if (Math.random() > 0.2) {
  a[i] = a[i].charAt(0).toUpperCase() + a[i].substring(1);
  }
 }
s = a.join(" ");

Here's an update now that you clarified:

var doIt = function (s, which) {
  var a = s.split(" ");
  a[which] = a[which].charAt(0).toUpperCase() + a[which].substring(1);
  return a.join(" ");
 }

Provided you can get the pattern definitively set, use Regex to find the pieces that need capitalizing. If you are using a dictionary, a state machine pattern is the best. For easy coding, the fastest is running through the words one at a time and finding those that fit the pattern. If perf is the main need, there are tricky ways to increase perf, including (at the extreme end) using binary.