Functions are like little pieces of functionality that we can run.

Here’s a function declaration:

function foo() {
  var a = b;

In this example, the name of the function is foo. The body of the function goes inside the curly brackets ({ and }).

If I want to call that function from somewhere else in my program, I would write:


I could also bind the function to an event, for example:


<button id="bar">Test</button>


document.getElementById('bar').onclick = foo;

Now, whenever the user clicks on the element with an id of bar, the function foo will be called.