JavaScript: The Definitive Guide, 6th Edition

Core JavaScript

This section is a tour of the JavaScript language, and also a tour of Part I of this book. After this introductory chapter, we dive into JavaScript at the lowest level: Chapter 2, Lexical Structure, explains things like JavaScript comments, semicolons, and the Unicode character set. Chapter 3, Types, Values, and Variables, starts to get more interesting: it explains JavaScript variables and the values you can assign to those variables. Here’s some sample code to illustrate the highlights of those two chapters:

// Anything following double slashes is an English-language comment.
// Read the comments carefully: they explain the JavaScript code.

// A variable is a symbolic name for a value.
// Variables are declared with the var keyword:
var x;                     // Declare a variable named x.

// Values can be assigned to variables with an = sign
x = 0;                     // Now the variable x has the value 0
x                          // => 0: A variable evaluates to its value.

// JavaScript supports several types of values
x = 1;                     // Numbers.
x = 0.01;                  // Just one Number type for integers and reals.
x = "hello world";         // Strings of text in quotation marks.
x = 'JavaScript';          // Single quote marks also delimit strings.
x = true;                  // Boolean values.
x = false;                 // The other Boolean value.
x = null;                  // Null is a special value that means "no value".
x = undefined;             // Undefined is like null.

Two other very important types that JavaScript programs can manipulate are objects and arrays. These are the subject of Chapter 6, Objects, and Chapter 7, ...