Introduction to JavaScript

Javascript is...

  • Not Java nor Java-like
  • A single-threaded, asynchronous (non-blocking), dynamically-typed, and weakly-typed language
  • An imperative language (primitive language) with some functional-like aspects and OOPS feature (enhanced in ES6)
  • An interpreted language

history of javascript

  • Created by Brendan Eich at Netscape for its browser, Navigator
  • JavaScript history names: Mocha -> LiveScript -> JavaScript -> ECMAScript
  • In today's world, ECMAScript is a standard whereas JavaScript is an implementation (will talk more about ECMAScript later)

single-threaded

  • There is one and only one thread called main thread handling tasks (what is a thread? think of it as worker in a factory)
  • JavaScript has been traditionally known as a single-threaded language, but modern JavaScript is no longer single-threaded thanks to web worker and service worker.

Async & non-blocking

  • In the browser environment, what things are blocking?
  • What could happen if code is blocking the browser?
  • Async is the savior

Dynamic typing & weak typing

  • Dynamic typing:
    • Type is determined at runtime
    • No need to specify type for a variable at declaration
  • Weak typing:
    • Type can be magically converted to another type at runtime

Imperative language

  • A.k.a. primitive language
  • JavaScript can also be functional and OOPS

Interpreted language

  • Code is interpreted at runtime, meaning that a runtime engine (like Chrome v8) needs to parse and compile your source code before it can execute it
  • Not performant compared to compiled language such as Go

ECMAScript

  • Stands for European Computer Manufacturer's Association
  • A standard that specifies core features for JavaScript
  • JavaScript is a well-known implementation of this standard
  • History standards: ES3, ES5
  • New standards: ES6 (a.k.a. ES2015)

data Types

  • Primitive types: boolean, number, string, null, undefined, symbol (new in ES6)
  • Object type: anything that is not primitive types, such as Array, Function

Hoisting

  • Hoisting is JavaScript's default behavior of moving all variable declarations to the top of the current scope (to the top of the current script or the current function)
  • A variable can be used before it has been declared
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