Javascript notes

notes.js

// Some stuff requires ES6

// Watch this first
// Philip Roberts: What the heck is the event loop anyway? | JSConf EU 2014 
// https://www.youtube.com/watch?v=8aGhZQkoFbQ

// Then read this
// https://rainsoft.io/gentle-explanation-of-this-in-javascript/

// https://strongloop.com/strongblog/higher-order-functions-in-es6easy-as-a-b-c/

// || returns the value from left side if it's true
true || false; // true
false || true; // true
// && returns the value from left side if it's false
true && false; // false
false && true; // false

// IIFE and closure
// IIFE is the (..)() part enclosing the function.
// !! This code will return function n, not the whole function !! Variable c is now a function that returns variable name. 
// This name-variable cannot be accessed otherwise. It's private.
// Without using IIFE, c is a function that contains the whole function, including variable name. This means that
// the name-variable is public. To return the name, you need to call c()();
let c = (function() {
  let name = "aha";
  
  return function n() {
    return name;
  }
  // It's also possible to return an object
  /* 
  return {
    n: function() { return name; },
    s: function(val) { name = val; }
  }
  // Now c is an object with two functions, n and s.
  // c.n(); // "aha";
  // c.s("okey");
  // c.n(); // "okey";
  */
})();
c(); // "aha"

// Object destructuring in function arguments
const d = { name: 'jack', age: 22, results: [1,2,3], works: true };
function printData({name, age, ...rest}) {
  console.log(name, age, rest);
}
printData(d); // jack 22 [object Object] => jack 22 Object {results: Array[3], works: true}

// Filter, Map, Reduce
const orig = [1,2,3,4,5];
const isEven = val => val % 2 == 0;
const double = val => val * 2;
const sum = (a,b) => a+b; // reduce(prev, next)

let work = orig.filter(isEven).map(double).reduce(sum);

console.log(orig); // 1,2,3,4,5
console.log(work); // 12