How JavaScript engines work

What is a JavaScript engine?

A JavaScript engine is a program that helps to convert JavaScript code into lower level code or machine code. The ECMAScript standard is followed by JavaScript engines. The job of these standards is to provide a definition of how JavaScript engines should work. It also tells it all the functions it should have.

If we generalize, high-level languages such as JavaScript, C, and FORTRAN have already been abstracted from machine languages. Compared to C or C++, JavaScript’s level of abstraction is further away from the machine level. C and C++are closer to hardware and other reasons that make them faster.

Compilation and interpretation

Compilation and interpretation are several methods commonly used to implement code in programming languages.

A compiler can be defined as a program that helps convert code. This conversion is for code execution that has already been written in any programming language (source language), converting to another programming language that you are targeting. They perform this task by translating the source code from high-level programming languages to low-level programming languages (i.e. machine languages).

The interpreter analyzes your source code line by line, instruction by instruction, and then directly executes the corresponding machine code on the target machine without any third-party involvement.

Although compilation and interpretation are two principles for achieving programming language implementation, they are also interrelated in some cases. This relationship arises because most systems that use interpretation do indeed perform some translation work. The translation work is also completed by the compiler.

If we talk about the category of JavaScript, then it belongs to the category of interpretation, even if it has already been technically compiled. Today’s modern JavaScript compilers perform real-time (JIT) compilation that occurs at runtime.

JavaScript engines connect to browsers and web servers, such as Node JS, so you should have permission to compile and execute JavaScript code at runtime.

Analysis of JavaScript Engine

The ECMA script specifies the process that browsers should implement JavaScript so that the program runs the same in each browser. It does not specify how JavaScript should run in these browsers. It depends on the supplier’s browser to determine this. Each browser provides you with a JavaScript engine that runs JavaScript code.

The Spider Monkey JavaScript engine is currently being used by Netscape browsers. This engine is defined as the basic interpreter for zero optimization. If you run your JavaScript code on this engine, it will run and work, but it will take more time.

The job of a JavaScript engine is to obtain JavaScript source code. Then compile it into binary instructions (machine code) that are easy for the CPU to understand.

In addition, the interpreter retrieves this bytecode and converts it into machine code. This machine code will further run on the hardware of the machine.

It works very similar to Java, but the generation of bytecode is done by programmers, and bytecode is widely shared rather than source code.

The job of a baseline compiler is to compile code as quickly as possible. It also generates less optimized byte code. Like the interpreter, it does not have optimized bytecode to use, so the speed of the application will be very slow. On the other hand, the application time will be very short.

The Spider Monkey JavaScript has been embedded into a complex machine. This is done to improve the efficiency of highly optimized machine code. It is currently being used in the Mozilla Firefox browser.

If we could choose to create a highly dynamic and interactive web application, developers would encounter issues when executing JavaScript. This is the issue that Google Chrome browser faces when displaying Google Maps on online platforms. In order to improve the performance of JavaScript, they provide a better solution, which we will discuss later in this article.

If the system in JavaScript is missing, the JavaScript engine will generate very little machine code. Therefore, based on the values already mentioned, JavaScript engines can intuitively understand the data types of variables and generate better code.