coding-practices.md

Use MAP or SET

The Map object holds key-value pairs and remembers the original insertion order of the keys. Any value (both objects and primitive values) may be used as either a key or a value.

The Set object lets you store unique values of any type, whether primitive values or object references.

import _ from "lodash";

const items2 = [
  {
    id: "unassigned",
    label: "Unassigned",
    color: "red",
    value: 245,
    active: false
  },
  {
    id: "new",
    label: "New",
    color: "blue",
    value: 54,
    active: false
  },
  {
    id: "inprogress",
    label: "In Progress",
    color: "purple",
    value: 78,
    active: false
  },
  {
    id: "pending",
    label: "Pending",
    color: "yellow",
    value: 12,
    active: false
  },
  {
    id: "resolved",
    label: "Resolved",
    color: "green",
    value: 245,
    active: false
  }
];

var youngest = _.chain(items2)
  .filter(o => o.active === false)
  .value();

console.log(youngest);

JS Array Methods That Mutate

Certain array methods will mutate the array they’re used on:

• push (add an item to the end)
• pop (remove an item from the end)
• shift (remove an item from the beginning)
• unshift (add an item to the beginning)
• sort
• reverse
• splice

Yep, JS Array’s sort is not immutable! It will sort the array in place. The easiest thing to do, if you need to use one of these operations, is to make a copy of the array and then operate on the copy. You can copy an array with any of these methods:

let a = [1, 2, 3];
let copy1 = [...a];
let copy2 = a.slice();
let copy3 = a.concat();

TIP

And one quick aside about sort (which has bitten me in the past) is that the compareFunction needs to return 0, 1, or -1. Not a boolean! Keep that in mind next time you’re writing a comparator.