In this lecture and in next few lecture, we are going to learn about how JavaScript programs are executed behind the scenes. This is a very important concept to learn about and every modern JavaScript developer should be aware of how JavaScript works behind the scenes.
Let’s start by understanding what JavaScript runtime is. Remember that, what we are going to learn now is very important concept. I will use this concept to explain many other JavaScript related topics.
A JavaScript runtime is an environment which provides all the necessary components in order to use and run a JavaScript program. These runtime environments can be a slightly different when we use JavaScript in browser and when we use it as a server-side language using NODE JS. However, the basic structure of a runtime environment remains same.
What is JavaScript Runtime consist of?
A JavaScript runtime in case of browser, consist of following components which forms a complete runtime environment:
• JavaScript engine
• Web API
• Callback Queue
• Microtask Queue.
Let’s talk about each of these components one by one in this lecture.