Essential JavaScript


A function is a set of instructions for the computer to run.

Functions can take in data, work with it, and return a result. The practice editor contains a function named returnFive that returns the value 5.

Try running the practice editor and see what happens.

Calling a Function

Functions are like recipes. Writing a recipe and following a recipe are two different things. Just because we write a recipe down on paper doesn't mean we automatically get food. We have to actually follow the recipe.

We just declared a function, but that's all we did. We just wrote our recipe down on paper.

In order to run the function (follow our recipe and get a result), we have to call it. To call a function, use the function's name with parentheses behind it.

Add returnFive() as a new line in the editor. See what happens.


Once we call the function, we actually get the return value of the function back. We see 5 in the results.

Functions are important because they allow us to reuse code. After we write a function once, we can use that function over and over again in other places in our code.

Learning Goals

Code Editor