JS .trim() is supported in basically everthing, except IE 8 and below.
If you want it to work with that, then, you can use JQuery, but it'll need to be <2.0.0 (as they removed support for IE8 in the 2.x.x line).
Your other option, if you care about IE7/8 (As you mention earlier), is to add trim yourself:
if(typeof String.prototype.trim !== 'function') {
String.prototype.trim = function() {
return this.replace(/^\s+|\s+$/g, '');
}
}