JavaScript is a scripting or programming language that allows you to implement complex features on web pages — every time a web page does more than just sit there and display static information for you to look at — displaying timely content updates, interactive maps, animated 2D/3D graphics, scrolling video jukeboxes, etc.

HTML is the markup language that we use to structure and give meaning to our web content, for example defining paragraphs, headings, and data tables, or embedding images and videos in the page.

CSS is a language of style rules that we use to apply styling to our HTML content, for example setting background colors and fonts, and laying out our content in multiple columns.

JavaScript is a scripting language that enables you to create dynamically updating content, control multimedia, animate images, and pretty much everything else. (Okay, not everything, but it is amazing what you can achieve with a few lines of JavaScript code.)

Over the past 20 years or so since when JavaScript was released, it has become the most popular programming language for web development today. You can understand the importance of JavaScript as a web development language from the fact that as per the recent reports, JavaScript is currently being used by more than 94 percent of all the websites.

JavaScript is a client-side programming language which helps web developer to do Web Application Development and make dynamic and interactive web pages by implementing custom client-side scripts.