Arrays and Objects

Introduction

So far each variable holds one value. Real programs handle many: a list of scores, a user with a name, an age and an email. JavaScript has two main tools for that: arrays and objects.

Arrays: ordered lists

An array holds values in order, inside square brackets. Each item has a position called an index, which starts at 0.

fruits[0] is the first item. length is the number of items.

Changing arrays

• push adds to the end, pop removes from the end.
• includes checks whether an item is there.
• join turns an array into a string.

You can change what is inside a const array. What const protects is the variable itself, which cannot be pointed at a different array.

Objects: named properties

An object stores values under names, called properties, inside curly braces.

• Read a property with a dot, person.name, or brackets, person["name"].
• Assign to change an existing property or add a new one.

Objects can hold functions

A function inside an object is called a method.

this inside a method refers to the object it belongs to. You will learn more about it in the advanced course.

Arrays of objects

The two combine into the shape of most real data: a list of things, each with properties.

Try it yourself

Create an array of three objects, each with a title and year for your favourite films or books. Then loop over the array and print each one as a sentence.

Summary

• Arrays are ordered lists, starting at index 0. Use push, pop, includes and join.
• Objects hold named properties. Use dot or bracket notation.
• An array of objects is the most common data shape.