Foundations Updated 2026-09 View as Markdown

Manipulating Arrays

Arrays can also function as a stack. The push and pop methods insert and remove variables from the end of an array.

Pushing and popping#

Arrays can also function as a stack. The push and pop methods insert and remove variables from the end of an array.

For example, let’s create an empty array and push a few variables.

let myStack = [];
myStack.push(1);
myStack.push(2);
myStack.push(3);
console.log(myStack);

This will print out:

1,2,3

After pushing variables to the array, we can then pop variables off from the end.

console.log(myStack.pop());
console.log(myStack);

This will print out the variable we popped from the array, and what’s left of the array:

3           // the result from myStack.pop()
1,2         // what myStack contains now

Queues using shifting and unshifting#

The unshift and shift methods are similar to push and pop, only they work from the beginning of the array. We can use the push and shift methods consecutively to utilize an array as a queue. For example:

let myQueue = [];
myQueue.push(1);
myQueue.push(2);
myQueue.push(3);

console.log(myQueue.shift());
console.log(myQueue.shift());
console.log(myQueue.shift());

The shift keyword will remove the variables of the array in the exact order they were inserted in, and the output will be:

1
2
3

The unshift method is used to insert a variable at the beginning of an array. For example:

let myArray = [1,2,3];
myArray.unshift(0);
console.log(myArray);       // will print out 0,1,2,3

Splicing#

Splicing arrays in JavaScript removes a certain part from an array to create a new array, made up from the part we took out. For example, if we wanted to remove the five numbers from the following array beginning from the 3rd index, we would do the following:

let myArray = [0,1,2,3,4,5,6,7,8,9];
let splice = myArray.splice(3,5);

console.log(splice);        // will print out 3,4,5,6,7
console.log(myArray);       // will print out 0,1,2,8,9

After splicing the array, it will only contain the part before and after the splicing. The splice is equal to all the variables between 3 and 7 (inclusive), and the remainder of the array, which contains all variables between 0 and 2 (inclusive), and 8 to 9 (inclusive).

What is the meaning of life?
42

let myArray = [true, "What is the meaning of life?"];
myArray.push(42);
myArray.shift();

console.log(myArray[0]);
console.log(myArray[1]);