JavaScript common function library based on prototype extension

The code is as follows:
/**
2 * Retrieve array element (prototype extension or overload)
3 * @param {o} retrieved element value
4 * @type int
5 * @returns element index
6 */
7 Array.prototype.contains = function(o) {
8 var index = -1;
9 for(var i=0;i<this.length;i++){if(this[i]==o){index = i;break;}}
return index;
}

/**
* date format (prototype extended or overloaded)
* format YYYY/yyyy/YY/yy means year
* MM/M month
* W/w week
* dd/DD/d/D date
* hh/ HH/h/H time
* mm/m minutes
* ss/SS/s/S seconds
* @param {formatStr} format template
* @type string
* @returns date string
*/
Date.prototype.format = function(formatStr){
var str = formatStr;
var Week = ['日','一','二','三','四','五','六'];
str=str.replace(/yyyy|YYYY/,this.getFullYear());
str=str.replace(/yy|YY/,(this.getYear() % 100)>9?(this.getYear() % 100).toString():'0' + (this.getYear() % 100));
str=str.replace(/MM/,(this.getMonth()+1)>9?(this.getMonth()+1).toString():'0' + (this.getMonth()+1));
str=str.replace(/M/g,this.getMonth());
str=str.replace(/w|W/g,Week[this.getDay()]);
str=str.replace(/dd|DD/,this.getDate()>9?this.getDate().toString():'0' + this.getDate());
str=str.replace(/d|D/g,this.getDate());
str=str.replace(/hh|HH/,this.getHours()>9?this.getHours().toString():'0' + this.getHours());
str=str.replace(/h|H/g,this.getHours());
str=str.replace(/mm/,this.getMinutes()>9?this.getMinutes().toString():'0' + this.ge…………………………………………………………………………

Detailed page: http://www.verydemo.com/demo_c98_i50643.html