PHP and Javascript 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 varfor 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`

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,
hi = "hello",
wrrrld = "world";

Technically, var is optional. But unless the variable
 was defined higher up in the scope chain , if youskip
 var, you end up with a global variable.

And you’ve learned, prob‐ably the hard way, that
 global namespace pollution is a sin. Additionally,
there are some subtle differences if you declare
 a global variable with and without var.

To cut a long story short, resist this temptation and
always use varto declare your variables.