Speaking JavaScript

Chapter 13. Statements

This chapter covers JavaScript’s statements: variable declarations, loops, conditionals, and others.

Declaring and Assigning Variables

var is used to declare a variable, which creates the variable and enables you to work with it. The equals operator (=) is used to assign a value to it:

var foo;
foo = 'abc';

var also lets you combine the preceding two statements into a single one:

var foo = 'abc';

Finally, you can also combine multiple var statements into one:

var x, y=123, z;

Read more about how variables work in Chapter 16.

The Bodies of Loops and Conditionals

Compound statements such as loops and conditionals have one or more “bodies” embedded—for example, the while loop:

while («condition»)
    «statement»

For the body «statement», you have a choice. You can either use a single statement:

while (x >= 0) x--;

or you can use a block (which counts as a single statement):

while (x > 0) {
    x--;
}

You need to use a block if you want the body to comprise multiple statements. Unless the complete compound statement can be written in a single line, I recommend using a block.

Loops

This section explores JavaScript’s loop statements.

Mechanisms to Be Used with Loops

The following mechanisms can be used with all loops:

break ⟦«label»⟧

Exit from a loop.

continue ⟦«label»⟧

Stop the current loop iteration, and immediately continue with the next one.

Labels

A label is an identifier followed by a colon. In front of a loop, a label allows you to break or continue that loop even from a loop nested ...