JavaScript lesson 18: Changing arrays: push, pop and more

What your child will learn

We are learning to add and remove items with push, pop, shift and unshift.

Success looks like

• I can add and remove items with push, pop, shift and unshift.
• I can check for an item with includes and indexOf.
• I can sort numbers correctly.

Key words

push · pop · includes · indexOf · sort · method

What to have ready

• A device with a web browser (the code runs in the browser – nothing to install)
• Paper for tracing
• A keyboard helps for typing code (a tablet or phone works too)

The big ideas (for the adult)

push(x) adds x to the END and gives back the new length. pop() removes the last item and gives it back. unshift and shift do the same at the START.

A const array can still change: const only means the name always points to the same array.

includes(x) is true or false; indexOf(x) gives the position or -1. Careful: sort() on its own sorts as TEXT, so 10 comes before 9. For numbers use sort((a, b) => a - b).

Worked example – see it

const list = ["mango", "grape", "bread"]
console.log(list.includes("grape"), list.includes("cherry"))

It prints:

true false

The lesson, step by step