11.5. Why Use Anonymous Functions?

At this point, you may be asking yourself Why am I learning anonymous functions? They seem strange, and their utility may not be immediately obvious. While the opinions of programmers differ, there are two main reasons why we think anonymous functions are important to understand.

11.5.1. Anonymous Functions Can Be Single-Use

There are many situations in which you will need to create a function that will only be used once. To see this, recall one of our earlier examples.


The anonymous function created in this example cannot be used outside of setTimeout.

setTimeout(function () {
   console.log("The future is now!");
}, 5000);

Defining an anonymous function at the same time it is passed as an argument prevents it from being used elsewhere in the program.

Additionally, in programs that use lots of functions---such as web applications, as you will soon learn---defining functions anonymously, and directly within a function call, can reduce the number of names you need to create.

11.5.2. Anonymous Functions Are Ubiquitous in JavaScript

JavaScript programmers use anonymous functions a lot. Many programmers use anonymous functions with the same gusto as that friend of yours who puts hot sauce on everything.

Just because an anonymous function isn't needed to solve a problem doesn't mean that it shouldn't be used to solve the problem. Avoiding JavaScript code that uses anonymous functions is impossible.

Any programming problem in JavaScript can be solved without using anonymous functions. Thus, the extent to which you use them in your own code is somewhat a matter of taste. We will take the middle road throughout the rest of this course, regularly using both anonymous and named functions.

11.5.3. Check Your Understanding


Explain the difference between named and anonymous functions, including an example of how an anonymous function can be used.