Javascript String substrCount(needle)

/**/*from  w  w w  .  j  a v  a 2s  .  com*/
@Name: String.prototype.substrCount
@Author: Paul Visco
@Version: 1.1 11/19/07 09/18/08
@Description: Returns the numbers of times a substring is found in a string
@Param: String needle The substring to search for within the string
@Return: Number The number of times the substring is found in the original string
@Example:
var myString = 'hello world on earth';

var answer = myString.substrCount('world');
//answer = 1;
*/
String.prototype.substrCount = function(needle){
 var cnt = 0;
 for (var i=0;i<this.length;i++) {
 if (needle == this.substr(i,needle.length))
  cnt++;
 } 
 return cnt;
};