Cắt bỏ khoản trắng trong javascript

function checkForm(){
var rs = false;
document.mainform.editor.value = editor.getHTML();
if(document.getElementById('servicename')!=null){
var str = document.getElementById('servicename').value;
str = trim(str);
if((str=="")||((str == null))){
alert('Please! input to service name!');
return false;
} else document.getElementById('servicename').value = str;
}
}
function trim(str) {
if(!str || typeof str != 'string')
return null;
return str.replace(/^[\s]+/,'').replace(/[\s]+$/,'').replace(/[\s]{2,}/,' ');
}
String.prototype.trim = function() {
if(!this || typeof this != 'string')
return null;
return this.replace(/^[\s]+/,'').replace(/[\s]+$/,'').replace(/[\s]{2,}/,' ');
}
_form id="mainform">
_textarea id="editor">empty textarea>
form>