Function Parameters and Return Values in JavaScript

JavaScript functions are an essential part of the language's syntax and allow developers to create reusable blocks of code. One of the key features of functions is the ability to accept parameters and return values. In this article, we will explore how functions can take inputs, process them, and produce outputs.

Function Parameters

Function parameters are variables declared within the function's parenthesis, which act as placeholders for values that will be passed into the function when it is called. These parameters allow us to pass different values to a function each time it is called, making our functions more versatile and adaptable.

To define parameters, we simply list them inside the parenthesis separated by commas. For example:

function greet(name, age) {
    console.log(`Hello ${name}, you are ${age} years old!`);

In the above code, name and age are the parameters of the greet function. When we call this function, we can pass actual values for these parameters, like this:

greet("John", 25);

This will output: "Hello John, you are 25 years old!" to the console.

Multiple parameters allow us to provide the function with the necessary data to perform specific tasks. They can be of any data type, including numbers, strings, arrays, or even other functions.

Return Values

While parameters allow us to pass data into a function, return values allow us to get data back from a function. A return statement inside a function specifies the value that the function should produce as its result. It also ends the execution of the function, returning control to the code that called it.

Consider the following example:

function add(x, y) {
    return x + y;

In this case, the add function takes two parameters (x and y), adds them together, and returns the result. We can store the return value in a variable or use it directly. For instance:

let sum = add(5, 3);
console.log(sum); // Output: 8

Similarly, we can use the return value of a function in other calculations or pass it as an argument to another function.

It's important to note that functions are not required to have parameters or return values. Some functions may only perform a set of actions without producing a result, while others may take inputs but not return anything. However, the flexibility of using parameters and return values enhances the power and usability of functions.


Function parameters allow us to pass values into a function, enabling it to handle different data each time it is called. Return values, on the other hand, provide a way to obtain a result from a function to use in further calculations or assignments. Understanding how to use function parameters and return values effectively is crucial for writing modular and reusable code in JavaScript.

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