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Wednesday, April 29, 2020

JavaScript Basic 2020

Learn what's new with JavaScript in 2020. It has changed a lot from the JavaScript you know.
  • JavaScript is interpreted as opposed to compiled
    • C is compiled
    • No need to declare variable types
    • Allows dynamic typing : given a variable there is no type associated with it until it is filled with value, it can be changed later. Some languages are not 
  • ES6 is the latest version of JavaScript full name is ECMAScript 6
    • Symbol
  • In new JavaScript languages semicolon ; is likely optional
  • JavaScript can check equality using double equal sign ==  , or triple equal sign  ===
    • == coerces the type
    • === requires to be exact, doesn't coerce the type 
  • Node command line runtime for JavaScript is built on V8 engine
  • typeof null --> returns object - one of those strange behaviors of JavaScript
  • JavaScript development is guided by ECMAScript standard. ECMA is pronounced Ehk-MA. E stands for Europe
  • You can think : the spec for JavaScript is written by ECMA
  • Each browser can have its own JavaScript engine, for example Chrome uses V8
  • Event Listener
    • Listening or subscribing events such as keydown 
    • aka the =Event handler
  • Modern JavaScript variations include Typescript, frequently used in Angular 
  • npm is the popular package manager for JavaScript
    • Has joined Github
    • In order words both Github and npm is now owned by Microsoft
  • Define a constant : const CONSTANT = 0.5
  • Enclose strings in double quotes or single quotes
  • Arrays can contain values as well as functions
    • const arr = ["value1",5, function(){console.log("Hello World")}]
      • Run the function arr[2]()
    • Can contain different types
    • Can access using indexing, starting from position zero
    • use array with for loop
for (let i = 0; i < arry.length : i++) {
    console.log(arr[i])
}

  • JavaScript allows trailing comma
  • Types
    • primitives: 
      • no methods attached?  immutable
        • boolean, string, null, number, symbol, undefined
        • Number includes both float and integer, there is no separate type
  • Sudden differences between undefined and null
  • JavaScript string
    • concatenation is implicit coercion or type casting, if we use str(variable) then that's explicit coercion
  • checking types of input using typeof, e.g. typeof undefined // --> undefined, type 5 // --> number
  • Try out JavaScript interactively using Chrome browser inspect element mode, or install node and call interactive JavaScript prompt. Use those two as a JavaScript interpreter
  • In general, undefined is returned if nothing specific is returned
  • JavaScript documentation by Mozilla https://developer.mozilla.org/en-US/docs/Web/javascript

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