<aside> ⚠️ This note serves as a reminder of the book's content, including additional research on the mentioned topics. It is not a substitute for the book. Most images are sourced from the book or referenced.

</aside>

All notes in this series

Infor & Preface

Chap 1 — What is JS?

What's With That Name?

• Not related with Java at all, not just a script but a programming language.
• "Java" → attract mostlty Java programmers, "Script" → light weight.
• Official name specified by TC39 as "ECMAScript" (ES).
• JS in browsers or Node.js is an implementation of ES2019 standard.
• Hosted by ECMA.
• Don't use "JS6" or "ES8", use "ES20xx" or "JS".

Language Specification

• Who decides a new version of JS? → TC39 (~50-100 members) by votes via 5 stages.
• There is just one JS in the wild (not multiple versions).
• Environments run JS: browsers, servers, robots, lightbulbs,....
• Not all are JS, eg. alert("Hello, JS!") or console.log() ← they're just APIs of JS environments.
  • There are many "JS-looking" APIs: fetch(), getCurrentLocation(), getUserMedia(),...
  • They follow JS rules but just "guests", not official JS specifications.
• Complain "JS is so inconsistent!" ← it's because the environment hehaviors work, not because of JS itself!
• Developer Tools (Inspect Element in Chrome, for example) are... tools for developers. They're NOT JS environment!
  • Something works in Dev Tool, doesn't mean JS compiler will understand it.

Many Faces

• Paradigm-level code categories
  • Procedural: organizes codes in a top-down, linear progression. ← eg. C
  • Object-oriented (OO/classes): organizes codes into classes. ← eg. Java/C++
  • Functional (FP): organizes codes into functions. ← eg. Haskell
  • JS is a multi-paradigm language. → "meaning the syntax and capabilities allow a developer to mix and match (and bend and reshape!) concepts from various major paradigms"

Backwards & Forwards

• Backwards compatibility:
  • Code from the past should still work today — "we don't break the web" (TC39)
  • Idea: JS developer can write code with confidence → their code won't stop working in new released versions.
  • Once it’s in JS, it can’t be taken out because it might break programs, even if we’d really, really like to remove it!
  • My idea to remember: old codes work with new engines but old engines may not work with new codes.