Recall JavaScript

The place where I look up regulary to refresh my mind about things I learn about JavaScript.

This document assumes you are familiar with JavaScript and just need to look up techniques or expections in JavaScript so as to refresh your memory. I write down whatever I find interesting while I'm learning about JavaScript, be it a simple thing or a very complex concept.

These notes are taken from the following learning materials:

• JavaScript.info by Ilya Kantor

Table of Contents

1. JavaScript Introduction
2. JavaScript Fundamentals

JavaScript Introduction

• 1.1 JavaScript Engines: there are many different JS engines that implements ECMA standards to run JS codes. Each of them has got their own code name.

  • V8: used in Chrome and in Node.js, built by Google.
  • SpiderMonkey: used in various Mozilla products, including Firefox, built by Mozilla.
  • Trident & Chakra: used in Internet Explorer, built by Microsoft
  • ChakraCore: used in Microsoft Edge, built by Microsoft
    • Note: Edge was later rebuilt as a Chromium-based browser and thus now uses V8.

• 1.2 How JS engines work: in a nutshell, the following steps are executed to acheive a running code:

  • Parse the script
  • Compile it to machine language
  • Run machine codes

• 1.3 Languages over JS: there are some languages that ultimately are transpiled to JavaScript.

  • TypeScript by Microsoft
  • Flow by Facebook
  • Dart by Google

• 1.4 ECMAScript: is JavaScript's own specification.

  • ECMA-262 contains the most in-depth, detailed and formalized information about JavaScript.
  • A new specification version is released every year.
  • Bleeding-edge features are called "stage-3" means they are almost standard and can be found at https://github.com/tc39/proposals.

JavaScript Fundamentals

• 2.1 Automatic semicolon insertion, in most cases, a newline implies a semicolon, but “in most cases” does not mean “always”! The rule is fully explained in the specification.

• 2.2 variable naming

  • When variable name contains multiple words, camelCase is commonly used.
  • Case matters; i.e. variables named apple and AppLE are two different variables.
  • Non-Latin letters are allowed, but not recommended.
  • Using different variables for different values can even help the engine optimize your code.

• 2.3 Data types

  • There are 8 basic data types in JavaScript.
    • Number: The number type represents both integer and floating point numbers. Infinity, -Infinity, and NaN are also of type number. NaN is sticky. Any further operation on NaN returns NaN.
    • BigInt:
    • String:
    • Boolean:
    • null:
    • undefined:
    • Object:
    • Symbol: