JavaScript cookie set and upadte

cookieManage.js

function increaseCookieValue(ckName){
	var siteCookie = document.cookie, cookieValue;
	if(siteCookie == null || !siteCookie.contains(ckName) || isNaN(getNumFromCookie(ckName))){
		cookieValue = 1
	}else{
		var num = getNumFromCookie(ckName);
		cookieValue = num+1;
	}
	return setCookie(cookieValue);
}

String.prototype.contains = function (text){
	for(var i=0;i<this.length-text.length;i++){
		if(this.substring(i,i+text.length)===text){
			return true;
		}
	}
	return false;
}

String.prototype.findIndex = function (text){
	for(var i=0;i<this.length-text.length;i++){
		if(this.substring(i,i+text.length)===text){
			return i;
		}
	}
	return -1;
}

function setCookie(cvalue) {
    var d = new Date();
    d.setTime(d.getTime() + (365*24*60*60*1000));
    var expires = "expires="+ d.toUTCString();
    document.cookie = "Count=" + cvalue + "; " + expires;
	return cvalue;
} 

function getNumFromCookie(cookieName){
	var ck = document.cookie;
	var start;
	for(var i=ck.findIndex(cookieName);i<ck.length;i++)
	{
		if(ck[i]==='='){
			start = i+1;
			break;
		}
	}
	for(var j=start; j<ck.length;j++)
	{
		if(ck[j]===';'){
			return parseInt(ck.substring(start,j));
		}else if(j===ck.length-1){
			return parseInt(ck.substring(start));
		}
	}
	return null;
}