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