js-hints-object

js-hints-object.js

// https://www.youtube.com/watch?v=5Kw4XVSb4P4

// Cloning objects, not deep! use clone for that https://gist.github.com/arturparkhisenko/db604e314ea8ff8ba065
const clonedR = {...obj};
const cloneOS = Object.assign({}, obj);

// Merging objects (also filling with defaults)
const mergedR = {...obj1, ...obj2};
const mergedOS = Object.assign({}, obj1, obj2);

// Non-destructively updating property `foo`
// with spread
const obj1 = {foo: 'a', bar: 'b'};
const obj2 = {...obj1, foo: 1}; // {foo: 1, bar: 'b'}
// or with Object.Assign
const obj2 = Object.assign({}, obj1, {foo: 1}); //  {foo: 1, bar: 'b'}

// Safely Accessing Deeply Nested Values In JavaScript
// https://medium.com/javascript-inside/safely-accessing-deeply-nested-values-in-javascript-99bf72a0855a
const props = {
  user: {
    posts: [
      { title: 'Foo', comments: [ 'Good one!', 'Interesting...' ] },
      { title: 'Bar', comments: [ 'Ok' ] },
      { title: 'Baz', comments: [] }
    ]
  }
};
// function:
const get = (p, o) =>
  p.reduce((xs, x) => (xs && xs[x]) ? xs[x] : null, o);
// let's pass in our props object...
console.log(get(['user', 'posts', 0, 'comments'], props));
// [ 'Good one!', 'Interesting...' ]
console.log(get(['user', 'post', 0, 'comments'], props));
// null

// DESTRUCTURING --------------------------------------------------------------

const cat = {sound: 'meow'};
const speak = ({sound}) => console.log(sound);
speak(cat); // => 'meow'

{
  // in general we have the same argument variable name as the object
  // property name, 
  // http://exploringjs.com/es6/ch_destructuring.html#sec_overview-destructuring 
  // {prop} is short for {prop: prop}

  // example short:
  let {sound} = cat;
  console.warn(sound);

  // example full:
  let sound;
  ({sound} = cat); // that's why i thought it'll destruct it at the argument stage, and make something like: 
  const speak = sound => console.log(sound);
}

// concat --------------------------------------------------------------
// https://twitter.com/YDKJS/status/922203387000709120/photo/1
// unfortunate syntax gotcha: can't use `...` spread in a ternary. a case where `[].concat(..)` is preferable.
let a = [1, 2, 3];
let b = [4, 5];
let c = [...a, Array.isArray(b) ? ...b : b]; // SyntaxError: Unexpected token ...
let d = [...a, ...(Array.isArray(b) ? ...b : b)]; // or
let e = a.concat(b);

// https://twitter.com/anatudor/status/923973815314583555
a.filter((c, i) => a.indexOf(c) == i);