Chris Rauber - Implementing String.trim() in Javascript

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Tuesday, May 13, 2008

Implementing String.trim() in Javascript

Curiously, the String class in javascript does not natively expose a trim() method. Not a problem! Since it is a dynamic language, javascript allows you the ability to crack open a class and add new functionality to it.

<script language="javascript" type="text/javascript">

String.prototype.trim = function() {
  return this.replace(/^\s+/,"").replace(/\s+$/,"");
}

var s = new String("  Test me!  ").trim();

alert("'" + s + "'");

</script>

The prototype keyword indicates that you are adding functionality to an existing class. In this case, we are adding a method called trim() to the String class that uses regular expressions to find any spaces (\s+ = one or more whitespace characters) at the beginning (^ = match at the START of a line) and then the end ($ = match at the END of a line) of the string, and replace the spaces we find with an empty string ("").