JavaScript for PHP Developers

Chapter 2. JavaScript Syntax

Just like PHP, JavaScript has a C-like syntax, so you’ll find it immediately familiar. This chapter goes over the basics, highlighting what’s similar and what’s different about variables, arrays, loops, conditions, and some miscellaneous (and slightly strange) operators.

Variables

To define a variable in PHP, you’d write:

// PHP
$n = 1;

The equivalent in JavaScript is:

// JavaScript
var n = 1;

There’s no dollar sign, just the name of the variable. Like in PHP, you don’t define variable types because the type is derived from the value. You use var for all types.

If you need a numeric type, you give your variable a numeric value. The same applies to booleans and strings:

var n = 1;       // number
var b = true;    // boolean
var s = "hello"; // string

You have the option of declaring a variable without initializing it with a value. In such cases, the variable is assigned the special value undefined:

var a;
a; // `a` has the special value `undefined`

Note

Redeclaring an existing variable doesn’t set the variable value back to undefined:

var a = 1;
var a;
// `a` is still 1

You can declare (and optionally initialize with a value) several variables with one var statement as long as you separate them with a comma and end with a semicolon:

var pi = 3.14,
    yeps = true,
    nopes,
    hi = "hello",
    wrrrld = "world";

Note

Technically, var is optional. But unless the variable was defined higher up in the scope chain (discussed in more detail in Chapter 3), if you skip var, you end up with a global ...