Table of contents

• Function declaration
• Arguments & Parameters
• Return
• Scope
• Hoisting
• Different type of functions
• The this keyword
• Conclusion
• Source material used

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In JavaScript you can create functions to write reusable blocks of code with functionality similar to most other programming languages, although, because of the nature of JavaScript, they might behave a bit differently, depending on the circumstances and the way you declare them.

Function declaration

In its simplest form a custom JavaScript function is declared as follows.

function myFunction() {

}

You can then call (use) this function later in your code with:

myFunction();

Now as it is, our function doesn’t actually do anything. So let’s add some functionality and delve into the subject of arguments and parameters.

Arguments and parameters

function myFunction(number1, number2) {
    console.log(number1 + number2);
}

The functionality we’ve added here is simply logging to the console the result of number1 + number2. As you can see these variables aren’t declared or defined anywhere else but between the function parenthesis. This is what are called parameters.

Parameters are variables entered as a part of the function definition. And these are the types of values we expect to be inserted when our function is called, like so:

myFunction(1,2);

The numbers 1 and 2 are passed into the parenthesis of the function when it is called, and are called arguments .

#function #javascript #this #custom-functions