1. JavaScript Engine According to Wikipedia

A JavaScript engine is a program or interpreter which executes JavaScript code.

To put it simply: JS engine is a program or interpreter that executes JS code. A JS engine can interpret as usual, or just-in-time compile from JS into bytecode.

Here are some famous JS engines:

SpiderMonkey - The ancestor of the JS engine, used on the world's first web browser - Netscape Navigator, currently being used on Firefox
Chakra - An old JS engine, originally used on Internet Explorer and compiled JScript, now used for Microsoft Edge
Rhino - An Engine written entirely in Java, also with a long history from Netscape Navigator, currently developed by the Mozilla Foundation
Google V8 - The most popular JS engine today, used on Chrome browser and NodeJS core

Engine includes 2 main components:

Memory Heap
Call Stack




2. Runtime
JS Runtime provides APIs for

3. Call Stack
JS is a single-threaded programming language, which means it has only 1 Call Stack. Therefore, at a time, JS only executes a single job.

The Call Stack is a data structure that stores the execution of the program. If a function is called, it is placed at the top of the stack. If a function terminates and returns a value, it will be removed from the stack. Each record in the Call Stack is called a Stack Frame.



When the above code is executed, it will call the function foo(). developer ebook download calls itself many times and has no stopping condition. With each execution step, a Stack Frame is added to the Call Stack. We will be met with the legendary stack overflow error

At that time, the browser will report an error

Executing single-threaded code can be very easy because you don't have to deal with complex situations like when dealing with multi-threaded environments, such as deadlocks. So what happens when a block of commands is processed too slowly?
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