Use native String.prototype.trim function wherever possible. Do not use String.trim. It is not part of ES5. Browsers are not required to implement it.

cross_browser_cross_javascript_string_trim.js

// dbjdbj@gmail.com
// Inspired also by http://github.com/dieseltravis
(function () {
   var trimLeft = /^\s+/, trimRight = /\s+$/;
  // Verify that \s matches non-breaking spaces (IE fails on this test)
  if ( !/\s/.test( "\xA0" ) ) {
    trimLeft = /^[\s\xA0]+/;
     trimRight = /[\s\xA0]+$/;
  }
   // Use native String.prototype.trim function wherever possible
   // Do not use String.trim. It is not part of ES5
  window.dbj_trim = "function" === typeof "".trim ? function( text ) {
      return ! text ? "" : String.prototype.trim.call( text.toString() );
    } :
    // Otherwise use our own trimming functionality
    function( text ) {
      return ! text ? "" : text.toString().replace( trimLeft, "" ).replace( trimRight, "" );
    }

}());