What Is JavaScript?

JavaScript is a programming language that makes websites, applications and mobile devices come to life. Without JavaScript, web pages would be just static text and images. Google Maps wouldn’t be able to detect a user’s location or Facebook wouldn’t update with new posts.

The Internet is essential to modern life, and without JavaScript, it wouldn’t function as well. It powers animation, dynamic content and form validation on web pages. It also interacts with APIs (Application Programming Interfaces), like Twitter’s.

A JavaScript-powered web page might ask for a user’s age and automatically check to see if the inputted number is appropriate. It could also respond to touch screen presses, cursor movements and mouse clicks to store data on the user’s device, such as previous site activity or preferences.

To execute JavaScript code, a browser uses an event loop and a single-threaded engine to process the codes in order. The engine also gathers profiling data to identify hot-code areas that are lagging and can be fixed by replacing the slow code with optimized machine code.

JavaScript can also be used to program other languages, such as C and Python. In addition, it can be used to connect to remote applications through APIs, including REST (Representational State Transfer) APIs that are remotely accessible through the Internet.

Variables and functions

In JavaScript, variables are containers for values of any data type. These are often used to store information, such as text or numbers.

You can define variables by using the var, let and const keywords. You can also use the keyword “global” to declare them outside the function scope.

Variables are also declared inside a function by using the arrow function keyword. These shorten the syntax for writing functions and make them easy to write.


JavaScript offers a variety of operators that can perform basic mathematical operations. Some of the most common are add, subtract and multiply. These are useful for comparing two or more numbers or strings to find their total value.

The most popular operator is multiply, which divides a number by another. It can be used to calculate a product’s price, for example.

When you’re learning to program in JavaScript, it’s important to understand the basic data types and how they work. These are the same data types you’d expect to learn in any other programming language, so it’s a good idea to have a basic understanding of them before moving on to more advanced topics.

You should also be familiar with function scope and block scope. These are the two main ways that you can declare a function and its variables in JavaScript.

Moreover, you should also know about function closures and arrow functions.

Closures are used to capture non-local variables by reference, so that they can be reused elsewhere in your program. They’re very helpful when you have multiple nested function calls or if you need to refer to non-local variables from other functions. They also help you to keep your code clean and concise.