javascript, utility string prototypes

string prototypes

String.prototype.startsWith = function(str)
{
	return (this.indexOf(str) === 0);
};

String.prototype.contains = function(str)
{
	return (this.indexOf(str, 0) !== -1);
};

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