Javascript

Javascript is a browser implementation of the ecmascript language specification

Node is v8 server side. Node is single threaded

Variables

let b = 'World'; // a mutable variable
const c = '!'; // a constant
var a = 'Hello'; // older "let", should generally be avoided

// functions are first class
function myFunction() {}
const myFunction = (...args) => {};

Functions

Functions are objects and can have properties and methods. Functions are first class.

Promises

A Promise is an object representing the eventual completion or failure of an asynchronous operation.

States:

• Pending
• Resolved
• Rejected

Once resolved or rejected it can never go back to pending

Callback functions are run after asynchronous code finishes…aka promises resolve

Context

this in a function is the object the represents the functions context.

/** call
 * a method placed on a function that calls the function
 * the first argument passed in is the new execution context (thisArg) */
const addToThis = (anyNumber) => {
    return this.num + anyNumber;
};
let obj = { num: 3 };
addToThis.call(obj, 7); //=> 10

OOP

The class is the context ES2015 syntactic suger is covering up JS’ actual inheritance model: Prototypal inheritance

class Dog extends Mammal{
    constructor(...args) {}
    static
    set
    get
    //etc...
}

Great OOP design: SOLID

Liskov’s substitution principle: Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program. Child classes can expand upon what they inherited, adding methods or extra properties, do not modify what they inherited.

FP

• Pure functions - deterministic
• Minimize side effects to the end of the application (rendering and such as)
• Higher order functions - functions are a data type that can be passed into things

gradually building something with currying
someFunction()()() => each function returns a function

• memoization
• keep data and behavior seperate