You are previewing Eloquent JavaScript.

Eloquent JavaScript

Cover of Eloquent JavaScript by Marijn Haverbeke Published by No Starch Press

Basic Data Structures

Before we can write this program, we will need to go over a few new language features.


Some JavaScript values have other values associated with them. These associations are called properties. Every string, for example, has a property called length, which refers to an integer, the amount of characters in that string.

Properties can be accessed in two ways, either with brackets or using dot notation:

var text = "purple haze";
→ 11
→ 11

The second way is a shorthand for the first, and it works only when the name of the property is a valid variable name—when it doesn’t have any spaces or symbols in it and does not start with a digit character.

Trying to read a property from the values null and ...

The best content for your career. Discover unlimited learning on demand for around $1/day.