JavaScript: The Missing Manual

Chapter 2. The Grammar of JavaScript

Learning a programming language is a lot like learning any new language: There are words to learn, punctuation to understand, and a new set of rules to master. And just as you need to learn the grammar of French to speak French, you must become familiar with the grammar of JavaScript to program JavaScript. This chapter covers the concepts that all JavaScript programs rely on.

If you’ve had any experience with JavaScript programming, many of these concepts may be old hat, so you might just skim this chapter. But if you’re new to JavaScript, or you’re still not sure about the fundamentals, this chapter introduces you to basic (but crucial) topics.

Statements

A JavaScript statement is a basic programming unit, usually representing a single step in a JavaScript program. Think of a statement as a sentence: Just as you string sentences together to create a paragraph (or a chapter, or a book), you combine statements to create a JavaScript program. In the last chapter you saw several examples of statements. For example:

alert('Hello World!');

This single statement opens an alert window with the message “Hello World!” in it. In many cases, a statement is a single line of code. Each statement ends with a semicolon—it’s like a period at the end of a sentence. The semicolon makes it clear that the step is over and that the JavaScript interpreter should move onto the next action.

Note

Officially, putting a semicolon at the end of a statement is optional, and some ...