React

Notes from Learning React, 2nd Edition by Porcello & Banks

Installation

// initialize a nodejs project (creates package.json)
$ npm init -y

// package manager 
$ npm install yarn

$ yarn install packagename

$ yarn remove packagename

JavaScript

Kangax compatibility table

Three ways to declare variables are

1. const
2. var
3. let

Template string

console.log(`${lastName}, ${firstName} ${middleName}`);

document.body.innerHTML = `
<section>
  <header>
      <h1>The React Blog</h1>
  </header>
  <article>
      <h2>${article.title}</h2>
      ${article.body}
  </article>
  <footer>
      <p>copyright ${new Date().getYear()} | The React Blog</p>
  </footer>
</section>
`;

Function declaration vs function expression

declarations are hoisted

const f = function() {
};

Arrow functions

const lordify = function(firstName) {
  return `${firstName} of Canterbury`;
};

// equals

const lordify = firstName => `${firstName} of Canterbury`;

Returning an object

DON'T FORGET PARENTHESES!

const person = (firstName, lastName) => ({
  first: firstName,
  last: lastName
});

console.log(person("Flad", "Hanson"));

Arrow functions and scope

const tahoe = {
  mountains: ["Freel", "Rose", "Tallac", "Rubicon", "Silver"],
  print: function(delay = 1000) {
    setTimeout(function() {
      console.log(this.mountains.join(", "));
    }, delay);
  }
};

tahoe.print(); // Uncaught TypeError: Cannot read property 'join' of undefined

console.log(this); // Window {}

To solve this problem:

const tahoe = {
  mountains: ["Freel", "Rose", "Tallac", "Rubicon", "Silver"],
  print: function(delay = 1000) {
    setTimeout(() => {
      console.log(this.mountains.join(", "));
    }, delay);
  }
};

tahoe.print(); // Freel, Rose, Tallac, Rubicon, Silver

Destructing objects

const sandwich = {
  bread: "dutch crunch",
  meat: "tuna",
  cheese: "swiss",
  toppings: ["lettuce", "tomato", "mustard"]
};

const { bread, meat } = sandwich;

console.log(bread, meat); // dutch crunch tuna

const sandwich = {
  bread: "dutch crunch",
  meat: "tuna",
  cheese: "swiss",
  toppings: ["lettuce", "tomato", "mustard"]
};

let { bread, meat } = sandwich;

bread = "garlic";
meat = "turkey";

console.log(bread); // garlic
console.log(meat); // turkey

console.log(sandwich.bread, sandwich.meat); // dutch crunch tuna

destructuring parameter

const lordify = ({ firstname }) => {
  console.log(`${firstname} of Canterbury`);
};

const regularPerson = {
  firstname: "Bill",
  lastname: "Wilson"
};

lordify(regularPerson); // Bill of Canterbury

const regularPerson = {
  firstname: "Bill",
  lastname: "Wilson",
  spouse: {
    firstname: "Phil",
    lastname: "Wilson"
  }
};

const lordify = ({ spouse: { firstname } }) => {
  console.log(`${firstname} of Canterbury`);
};

lordify(regularPerson); // Phil of Canterbury

Destructuring arrays

const [firstAnimal] = ["Horse", "Mouse", "Cat"];

console.log(firstAnimal); // Horse

const [, , thirdAnimal] = ["Horse", "Mouse", "Cat"];

console.log(thirdAnimal); // Cat

Object literal enhancement

const name = "Tallac";
const elevation = 9738;

const funHike = { name, elevation };

console.log(funHike); // {name: "Tallac", elevation: 9738}

const name = "Tallac";
const elevation = 9738;
const print = function() {
  console.log(`Mt. ${this.name} is ${this.elevation} feet tall`);
};

const funHike = { name, elevation, print };

funHike.print(); // Mt. Tallac is 9738 feet tall

old vs. new: object syntax

// Old
var skier = {
  name: name,
  sound: sound,
  powderYell: function() {
    var yell = this.sound.toUpperCase();
    console.log(`${yell} ${yell} ${yell}!!!`);
  },
  speed: function(mph) {
    this.speed = mph;
    console.log("speed:", mph);
  }
};

// New
const skier = {
  name,
  sound,
  powderYell() {
    let yell = this.sound.toUpperCase();
    console.log(`${yell} ${yell} ${yell}!!!`);
  },
  speed(mph) {
    this.speed = mph;
    console.log("speed:", mph);
  }
};

Spread operator

const peaks = ["Tallac", "Ralston", "Rose"];
const canyons = ["Ward", "Blackwood"];
const tahoe = [...peaks, ...canyons];

console.log(tahoe.join(", ")); // Tallac, Ralston, Rose, Ward, Blackwood

Getting last element:

const peaks = ["Tallac", "Ralston", "Rose"];
const [last] = peaks.reverse();

console.log(last); // Rose
console.log(peaks.join(", ")); // Rose, Ralston, Tallac

Getting the rest of elements:

const lakes = ["Donner", "Marlette", "Fallen Leaf", "Cascade"];

const [first, ...others] = lakes;

console.log(others.join(", ")); // Marlette, Fallen Leaf, Cascade

function parameters:

function directions(...args) {
  let [start, ...remaining] = args;
  let [finish, ...stops] = remaining.reverse();

  console.log(`drive through ${args.length} towns`);
  console.log(`start in ${start}`);
  console.log(`the destination is ${finish}`);
  console.log(`stopping ${stops.length} times in between`);
}

directions("Truckee", "Tahoe City", "Sunnyside", "Homewood", "Tahoma");

combining objects:

const morning = {
  breakfast: "oatmeal",
  lunch: "peanut butter and jelly"
};

const dinner = "mac and cheese";

const backpackingMeals = {
  ...morning,
  dinner
};

console.log(backpackingMeals);

// {
//   breakfast: "oatmeal",
//   lunch: "peanut butter and jelly",
//   dinner: "mac and cheese"
// }

Asynchronous requests

Simple promises with fetch

fetch("https://api.randomuser.me/?nat=US&results=1")
  .then(res => res.json())
  .then(json => json.results)
  .then(console.log)
  .catch(console.error);

Async/Await

const getFakePerson = async () => {
  try {
    let res = await fetch("https://api.randomuser.me/?nat=US&results=1");
    let { results } = res.json();
    console.log(results);
  } catch (error) {
    console.error(error);
  }
};

getFakePerson();

Building Promises

const getPeople = count =>
  new Promise((resolves, rejects) => {
    const api = `https://api.randomuser.me/?nat=US&results=${count}`;
    const request = new XMLHttpRequest();
    request.open("GET", api);
    request.onload = () =>
      request.status === 200
        ? resolves(JSON.parse(request.response).results)
        : reject(Error(request.statusText));
    request.onerror = err => rejects(err);
    request.send();
  });

getPeople(5)
  .then(members => console.log(members))
  .catch(error => console.error(`getPeople failed: ${error.message}`))
);

Classes

prototypical inheritance

function Vacation(destination, length) {
  this.destination = destination;
  this.length = length;
}

Vacation.prototype.print = function() {
  console.log(this.destination + " | " + this.length + " days");
};

const maui = new Vacation("Maui", 7);

maui.print(); // Maui | 7 days

ES2015 way of declaring class

class Vacation {
  constructor(destination, length) {
    this.destination = destination;
    this.length = length;
  }

  print() {
    console.log(`${this.destination} will take ${this.length} days.`);
  }
}

const trip = new Vacation("Santiago, Chile", 7);

trip.print(); // Chile will take 7 days.

Simple inheritance

class Expedition extends Vacation {
  constructor(destination, length, gear) {
    super(destination, length);
    this.gear = gear;
  }

  print() {
    super.print();
    console.log(`Bring your ${this.gear.join(" and your ")}`);
  }
}

const trip = new Expedition("Mt. Whitney", 3, [
  "sunglasses",
  "prayer flags",
  "camera"
]);

trip.print();

// Mt. Whitney will take 3 days.
// Bring your sunglasses and your prayer flags and your camera

ES6 Modules

A module is a peice of reusable code that can easily be incorporated into other JavaScript files without causing variable collisions.

In text-helpers.js, two functions are exported:

export const print(message) => log(message, new Date())

export const log(message, timestamp) =>
  console.log(`${timestamp.toString()}: ${message}`)

Exporting only one variable from a module using export default

export default new Expedition("Mt. Freel", 2, ['water","snack"]);

Consuming using the import command

import { print, log } from "./text-helpers";
import freel from "./mt-freel";

print("printing a message");
log("logging a message");

freel.print();

scoping under different name:

import { print as p, log as l } from "./text-helpers";

p("printing a message");
l("logging a message");

import everything

import * as fns from './text-helpers`

CommonJS

the module pattern that is supported by all versions of Node, "Modules"

e.g.

const print(message) => log(message, new Date())

const log(message, timestamp) =>
console.log(`${timestamp.toString()}: ${message}`}

module.exports = {print, log}

CommonJS does not support an import statement; modules are mported with the require function

const { log, print } = require("./txt-helpers");