This should do the trick:
function humanize(str) {
var i, frags = str.split('_');
for (i=0; i<frags.length; i++) {
frags[i] = frags[i].charAt(0).toUpperCase() + frags[i].slice(1);
}
return frags.join(' ');
}
console.log(humanize('humpdey_dumpdey'));
// > Humpdey Dumpdey
repl
http://repl.it/OnE
Fiddle:
http://jsfiddle.net/marionebl/nf4NG/
jsPerf:
Most test data: http://jsperf.com/string-transformations
All versions plus _.str: http://jsperf.com/string-transformations/3