JavaScript Engine and JUST-IN-TIME Compiler

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In this lecture, lets understand how a JavaScript program get’s executed by the browser. In the last lecture, we learned that every browser has a JavaScript engine which is responsible for executing JavaScript code. So, in this lecture, you will learn all the steps involved in executing a JavaScript program by JavaScript engine.

What is machine code?
The programs which we write using any programming language like C, Java, C++, JavaScript etc. are called as high-level language. A high-level language is human readable.

A Compute processor only understands 0s and 1s. It does not understand the high-level programming languages like C or JavaScript. So, ultimately all the programs, no matter which programming language you are using, must be converted to 0s and 1s in order to execute it. This converted code is called as machine code.

We cannot write a computer program in machine code by ourselves. It is practically impossible. That’s why, we use high-level languages to write a program and then convert is to machine code using some tools in order to execute it.

The conversion of high-level language to machine code can be done by using compilation or interpretation. Let's understand these concepts in detail in this lecture.