Javascript Global variables

Method 1: Explicitly declare it outside of any function scope:

var g; // This is global

Method 2: Implicitly use a global variable by not using 'var' inside the function scope:

function x() { var a = "bye"; // This is only defined in the scope of x g = "hello"; // g was not var'ed, so it's a global } x(); // Run x alert(g); // alerts "hello" because g is global alert(a); // a is undefined

Method 3: Define a variable in the window scope: 

function x() { window.g = "hello"; } x(); alert(g);