Quick JavaScript tip #2: declare global variables from a function

In JavaScript, variables declared using var are local if declared from within a function, or otherwise global. That means that a variable declared inside a function can only be accessed from within that function.
Here's an example:

var x = "Hello World"; function myFunc() { var y = "Hi"; console.log(x); // "Hello World" console.log(y); // "Hi" } console.log(x); // "Hello World" console.log(y); // Uncaught ReferenceError: y is not defined  

But once in a while, you'll find yourself having to declare a global variable from a function. How can that be achieved? Let's start by understanding how global variables work.

When you declare a global variable in JavaScript, it actually creates a property of the window object. Here's an example:

var x = "Hello World"; console.log(x); // "Hello World" console.log(window.x); // "Hello World" 

This means that to declare a global variable from a function, you can manually set it as a property of the window object, like so:

function myFunc() { window.x = "Hello World"; } console.log(x); // "Hello World"