Writing a JavaScript code in correct approach can be fun instead of terrifying. In this tutorial we will see shift(), unshift() and push(), pop() are the methods of JavaScript that allows us to add remove elements. 
Lets discuss all these metnods one by one :

Shift() :

This method is similar to pop() method, the only difference is that it works at the beginning of the array. It delete the first element from the given array and returns it.

Example :

// Creating a test array
var data = [ "A", "B", "C" ];
// Delete the element from the beginning of the array.
 data.shift();

Unshift() :

This method is similar to push() method, the only difference is that it works at the beginning of the array. It add one or more elements to the beginning of an array.

Example :

// Creating a test array
var data = [ "X" ];
// Add the element at the beginning of an array.
data.unshift( "B", "C" ); 

Push() :

This method can add one or more elements at the end of an array.

Example :

// Creating a test array
var data = [ "X" ];
// Add the element at the end of an array.
data.push( "B", "C" ); 

Pop() :

This method removes the last element from the given array and returns it.

Example :

// Creating a test array
var data = [ "A", "B", "C" ];
// Delete the element from the end of an array.
data.pop();