Ref

1. Javascript this

What is this

• this in Javascript refers to the context of the statement in which it is being executed.

Refs

1. JavaScript Use Strict

Refs

1. 关于前端模块化 CommonJS、AMD、CMD、ES6中模块加载
2. MDN - Javascript Modules

What is a Javascript Module ?

Just a javascript file which can import functionality from other and export its own functionality.

(BLOG STILL IN PROGRESS)

Refs

1. Avoiding Memory Leaks in Node.js: Best Practices for Performance

What is a memory leak ?

Memory allocated but not freed.

(THIS BLOG IS STILL IN PROGRESS)

Refs

1. Typesript
2. Why create Typescript
3. Typescript Handbook Intro
4. Typescript入门教程
5. Javascript class
6. Type Declarations
7. What is DefinitelyTyped?
8. Ambient Modules

What is typescript ?

A strongly typed programming language that builds on JavaScript.

Reference:

1. A conclusion of Javascript running mechanism
2. Detailed explanation of Javascript asynchronism
3. JavaScript Event Loop And Call Stack Explained

Sinle-threaded Javascript

A running chrome consists of multiple process. Each tab is an isolated process.

A tab process consisits of multiple threads. Among them the important ones includes:

1. Rendering thread. Renders DOM.
2. Javascript engine thread. Runs Javascript. Note that when Javascript engine thread runs, rendering thread hangs. Because Javascript engine thread can manipulate DOM and rendering requires a consistent DOM.
3. Event thread. Handles event loop.
4. Timer thread. Handles timer methods like setTimeout, setInterval. Timer thread should be stand-alone as running of other function may affect timing accuracy.

Asynchronism

Javascript, well-known for its asynchronism.
Synchronous functions runs and gets result. When function is slow (e.g. has file I/O or web request operations), it waits.
Asynchronous functions runs and expects result. The function does not wait for result, instead it leaves a callback function there to handle future result, and it moves on.
Asynchronism makes Javascript run without idle time. That’s why javascript is fast.

Event loop and call stack

Browsers gives us Web APIs to handle callbacks. Functions like AJAX, setTimeout call these APIs.
Web APIs push callbacks into callback queue. Callbacks wait to be executed in the future.
Event loop watches call stack and callback queue. If call stack is empty, event loop takes one callback from callback queue and javascript engines executes the callback.

Queues

Callback queue is not only one but two queue: macrotask queue and microtask queue.
Everytime event loop is triggered, it takes all microtasks and one macrotask. Microtasks are executed first.
Macrotasks: setTimeout, setInterval, setImmediate, I/O operations, UI rendering
Microtasks: Promise, process.nextTick, MutationObserver