function substr_count (haystack, needle, offset, length) {
	    var pos=0, cnt=0;
	 
	    haystack += '';
	    needle += '';
	    if (isNaN(offset)) {offset=0;}
	    if (isNaN(length)) {length=0;}
	    offset--;
	 
	    while ((offset = haystack.indexOf(needle, offset+1)) != -1){
	        if (length > 0 && (offset+needle.length) > length){
	            return false;
	        } else{
	            cnt++;
	        }
	    }
	 
	    return cnt;
	}
	
	function randomKey(keylength){
		var characters='0123456789';
		var key = '';
		var i = 0;
		var randomnumber = 0;
		
		while( i < keylength ) {
			i++;
			randomnumber = Math.floor(characters.length*Math.random());
			key += characters.substring(randomnumber,randomnumber + 1);
		}

		return 'N'+key;
	}