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Home > Forums > Programmers > Web Development > Javascript > FAQs

Javascript FAQ

Strings

trim(), startsWith() and endsWith() in JavaScript?
faq216-6620
Posted: 17 Apr 07 (Edited 17 Apr 07)

All programmers who use JavaScript at some stage get frustrated searching for some standard functions that are simply not built into JavaScript! Also if you manage to write your own version for it, the call isn't as neat as the standard ones.

eg. calling the in-built substr() function would look something like myVar.substr(x, y) but if you wrote your own version (may be function substr2(str, x, y)) you'll have to call it as

CODE

myVar = substr2(myVar, x, y); //Your function
myVar = myVar.substr(x, y); //built-in function

Not so elegant is it?
Well, here is a way you could BIND your functions to the data type and call them like in-built functions… here's how:

Trim function, trims all leading and trailing spaces:

CODE

String.prototype.trim = function(){return
(this.replace(/^[\s\xA0]+/, "").replace(/[\s\xA0]+$/, ""))}

startsWith to check if a string starts with a particular character sequecnce:

CODE

String.prototype.startsWith = function(str)
{return (this.match("^"+str)==str)}

endsWith to check if a string ends with a particular character sequecnce:

CODE

String.prototype.endsWith = function(str)
{return (this.match(str+"$")==str)}

All these functions once loaded will behave as built-in JavaScript functions. Here are few examples:

CODE

var myStr = “  Earth is a beautiful planet  ”;
var myStr2 = myStr.trim();  
//==“Earth is a beautiful planet”;

if (myStr2.startsWith(“Earth”)) // returns TRUE

if (myStr2.endsWith(“planet”)) // returns TRUE

if (myStr.startsWith(“Earth”))
// returns FALSE due to the leading spaces…

if (myStr.endsWith(“planet”))
// returns FALSE due to trailing spaces…
Summary: Any function you think will be needed on a data type level can be implemented in this way… you don’t always need to use regular expressions for this but it does make it really compact.

Let me know if this was useful!thumbsup2

Enjoy scripting…noevil
Jay

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