How to Pass a Function as an Argument in JavaScript

Learn how to effectively pass functions with parameters to other functions in JavaScript, along with a detailed explanation and examples.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Pass a function with parameter as an argument to another function in JavaScript

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering Function Passing in JavaScript

JavaScript is a versatile language that allows developers to create complex functionalities with relative ease through its first-class functions. However, if you are just starting out, you may find yourself puzzled when trying to pass functions as arguments to other functions. If you're facing an issue with passing a function with parameters, you're not alone. In this guide, we will tackle this common problem and guide you through a solution step by step.

The Problem at Hand

Consider this scenario: you want to execute a function x while also passing parameters to it within another function called write. Here's the code example that was initially causing some confusion:

[[See Video to Reveal this Text or Code Snippet]]

When you attempt to run this code, you may encounter an error that may look something like this:

[[See Video to Reveal this Text or Code Snippet]]

The error arises because you're incorrectly trying to pass the function's return value instead of the function itself. Let's break down the solution to help you successfully pass functions as parameters.

Understanding Function Passing

What Are First-Class Functions?

In JavaScript, functions are treated as first-class citizens. This means:

You can assign functions to variables.

You can pass functions as arguments to other functions.

You can return functions from other functions.

Fixing the Code

To correctly use a function as an argument, you must pass the function without invoking it (i.e., without parentheses). Let's modify your write function call accordingly. Here’s how it can be done:

[[See Video to Reveal this Text or Code Snippet]]

In the revised code above, we call write with a as an argument, allowing us to pass the number 12 when x is called inside write().

Example of Function Passing

To further illustrate this concept, let's look at a simple example of how to pass functions that return values:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Example:

pass1 takes a value and returns a string.

pass2 returns a simple greeting.

receive_pass asks for two functions, calls them, and concatenates their results.

Conclusion

Passing functions as arguments to other functions opens up new avenues for code modularity and reusability. You can control the flow of your program and create highly interactive applications simply by leveraging this feature. If you find yourself needing to pass parameters to functions you pass as arguments, remember to pass the function reference itself and then call it with the desired parameters later.

Remember, as always, practice is key to mastering JavaScript. Happy coding!