DevelopmentJavaScript | 2 Min Read

JavaScript Fundamentals: First Class Functions

Functions are known as first class citizens in JavaScript, here's exactly what that means.

Functions are First Class Citizens

  • Meaning you can treat functions like any other variable in the language.
  • For example, you can pass a function as an argument to another function or a function can be returned by another function and assigned to a variable.

Storing a function in a variable.

1const example = () => {
2 console.log("This is an example");
3};
jsx

Invoking the function by using the variable it was stored in.

1example();
jsx

Passing a function as a variable

1function sayName() {
2 return "Coner";
3}
4
5function shout(text) {
6 return text.toUpperCase();
7}
jsx

We call `sayName()` which returns 'Coner' this is then immediately passed to shout() which returns it in the upper case.

1console.log(shout(sayName()));
jsx

Returing a function

If we want to invoke the function returned from another function we have a couple of options:

Option 1

1const sayName = function () {
2 return function () {
3 console.log("Coner");
4 };
5};
jsx

But, directly invoking our function doesn't yeild the result we wanted.

1sayName(); // Doesn't return 'Coner' instead directly returns the function.
jsx

To achieve the result we want of logging out 'Coner', we have store our function into another variable and invoke that.

1const func = sayName();
2
3func(); // 'Coner'
jsx

Option 2

1const sayName = function () {
2 return function () {
3 console.log("Coner");
4 };
5};
jsx

If we want to avoid using the variable method shown above we can use the double parentheses method to invoke the parent function and then the child function it returns which gives us the result we were after.

1sayName()(); // 'Coner'
jsx


Content

Latest Blog Posts

Below is my latest blog post and a link to all of my posts.

View All Posts

Content

Latest Video

Here is my YouTube Channel and latest video for your enjoyment.

View All Videos
Get more clients by this doing 1️⃣ thing!

Get more clients by this doing 1️⃣ thing!

Contact

Join My Newsletter

Subscribe to my weekly newsletter by filling in the form.

Get my latest content every week and 0 spam!