String.prototype.left = stLeft;
String.prototype.right = stRight;
String.prototype.digits = stDigits;

/* stDigits(cnt, chr); metoda objektu String.digits()
metoda vraci string na pocet znaku
parametry:
cnt - delka znaku vystupu
chr - znak ktery se doplnuje (nepovinny = "")
*/
function stDigits(cnt, chr) {
	var i, str = "";

	if ( this.length == cnt ) return this;
	if ( !chr ) chr = "";
	
	for ( i=1;i<=cnt;i++ ) {
		if ( i > this.length ) str = chr + str;
		else str = this.substr(this.length - i, 1) + str;
	}
	return str;
}

/* stLeft(cnt); metoda objektu String.left()
metoda vraci cnt pocet znaku zleva
*/
function stLeft(cnt) {
	return this.substr(0, cnt);
}

/* stRight(cnt); metoda objektu String.right()
metoda vraci cnt pocet znaku zprava
*/
function stRight(cnt) {
	return this.substr(this.length - cnt);
}