JavaScript Functions

(Lesson 3.0) - Introduction to JavaScript Functions

In JavaScript, functions are reusable blocks of code that can be defined and called by their name. They can accept input (in the form of parameters) and return output (in the form of a return value). Functions are an essential part of any programming language, helping to organize and structure your code.

Defining and Calling Functions

To define a function in JavaScript, you can use the function keyword followed by the function name, a list of parameters enclosed in parentheses, and a block of code enclosed in curly braces.

Here's an example of a simple function definition:

function greet(name) {
  console.log("Hello, " + name + "!");
}

Calling Functions

To call a function, simply use its name followed by the arguments enclosed in parentheses:

greet("John"); // Output: "Hello, John!"

Working with Function Parameters and Arguments

Function Parameters

Parameters are variables that are used to pass input to a function. When defining a function, you can specify one or more parameters in the function declaration.

Function Arguments

When calling a function, you can provide values (called arguments) for those parameters.

In the example below, the add function has two parameters: a and b.

function add(a, b) {
  return a + b;
}

let sum = add(2, 3);
console.log(sum); // Output: 5

Anonymous Functions and Arrow Functions

Anonymous Functions

An anonymous function is a function without a name. They are often used in situations where a function is only needed once, such as when passing a function as an argument to another function.

setTimeout(function() {
  console.log("Execute later after 1 second");
}, 1000);

Arrow Functions

Arrow functions are a more concise way of writing anonymous functions. They were introduced in ECMAScript 6 (ES6) and have a shorter syntax compared to regular function expressions. Here's the same setTimeout example using an arrow function:

setTimeout(() => {
  console.log("Execute later after 1 second");
}, 1000);

Arrow functions can also have a shorter syntax for functions with a single expression:

const add = (a, b) => a + b;

let sum = add(2, 3);
console.log(sum); // Output: 5

In this JavaScript tutorial, we have covered the basics of JavaScript functions, including defining and calling functions, working with parameters and arguments, and using anonymous functions and arrow functions. By understanding and utilizing functions in your code, you can create more organized, efficient, and reusable JavaScript programs. Click here to go back to our home page.