Jay Kanakiya's Blog

Every object in javascript has got a prototype method which basically adds new methods to the base object which then can be called on instance objects.

Comparing with other languages , constructor functions are classes and the properties of the prototype (i.e. of the object referenced by the constructor function’s prototype property) as shared members, ie members which are the same for each instance. In class-based systems, methods are implemented the same way for each instance, so methods are normally added to the prototype, whereas an object’s fields are instance-specific and therefore added to the object itself during construction.

A simple example

Type this in Chrome Devtools console :

function Animal() {} // This is a first class functional object
Animal.prototype.speak = function() { console.log('OK'); } //Add a prototype function
var cat = new Animal(); //Creates a new Animal
cat.speak(); // Will call that function and print OK

In the above example we first defined the constructor function and then added speak function to it.
We then initialized cat as an Animal and called the that function on it.

Another Example

//Define a functional object to hold Animal
var Animal = function(name) {
    this.name = name;
};

//A new getter for that name
Animal.prototype.getName = function() {
    return this.name;
};

//Create a new object of type Animal
var cat = new Animal("Kitty");

//alert(cat.getName()); will use the getter

//This is where we add the speak function to Animal
Animal.prototype.speak = function() {
    alert('Hello, my name is ' + this.getName());
};

//Call the new method on cat
cat.speak();

When you will run the above code in devtools console , you will get an alert saying My name is Kitty.
In the above example , we created the instance object then added a method to the base , and then called the new method on the instance object.
This is how Inheritance works in javascript.

Sources :

http://stackoverflow.com/questions/572897/how-does-javascript-prototype-work
http://ejohn.org/apps/learn/#65

The splice() method of Array in javascript changes the content of an array, adding new elements while removing old elements.
If you specify a different number of elements to insert than the number you’re removing, the array will have a different length at the end of the call.

The Syntax is

array.splice(index , howMany[, element1[, ...[, elementN]]])

where

index : Index at which to start changing the array. If greater than the length of the array, no elements will be added or removed. If negative, will begin that many elements from the end.

howMany : An integer indicating the number of old array elements to remove. If howMany is 0, no elements are removed. In this case, you should specify at least one new element. If howMany is greater than the number of elements left in the array starting at index, then all of the elements through the end of the array will be deleted. If no howMany parameter is specified (second syntax above, which is a SpiderMonkey extension), all elements after index are removed.

element1, …, elementN : The elements to add to the array. If you don’t specify any elements, splice simply removes elements from the array.

This method returns an array containing the removed elements. If only one element is removed, an array of one element is returned. If no elements are removed, an empty array is returned.

Example Usages of .splice :-

1.To prepend an element at the start of an array.

Type this in your Devtools console

var array = [1,2,3,4] //We define the initial array
->undefined
array.splice(0,0,5) //index is 0, howmany is 0 and element is 5
->[]
array
->[5, 1, 2, 3, 4]
array.splice(0,0,6,7)//You can prepend n elements
->[6, 7, 5, 1, 2, 3, 4]

2.To remove the first element of an array.

To remove the first element from array ,

array.splice(0,1)

Type this in Devtools console :

array = [1,2,3,4]
->[1, 2, 3, 4]
array.splice(0,1)
->[1]
array
->[2, 3, 4]

Similarly to remove n elements from the start of an array :

array.splice(0,n)//n is no. of elems

3.Add and Remove elements from array

Let assume we want to add as well as remove elements from array at the same time
Consider code :
cities.splice(2,1,"Mumbai","Nagpur")

The index is 2 i.e. the 3rd element,
howmany is 1 ,i.e 1 element will be removed ,
“Mumbai”,”Nagpur” will get added at index 2.

Type this in console :-

var cities = ["Pune", "Bangalore", "Delhi", "Kolkata"]
->undefined
cities.splice(2,1,"Mumbai","Nagpur")
->["Delhi"]
cities
->["Pune", "Bangalore", "Mumbai", "Nagpur", "Kolkata"]

Sources

MDN splice