Add Method to Built-in Javascript Object

You can use prototype property to add method to built-in Javascript objects

I am going to add inArray() to Array object in Javascript

Array.prototype.inArray=function(value){
    for(var i=0;i<this.length;i++){
        if(this[i]===value){
            return true
        }
    }
    return false
}

var numbers =[1,2,3,4,5,6,7,8]

console.log(numbers.inArray(9))

So number 9 is not array and you will get the output false