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Notes from Learning React, 2nd Edition by Porcello & Banks
Notes from '''Learning React, 2nd Edition''' by Porcello & Banks and other sources


= Installation =
= Installation =
Line 86: Line 86:


== Arrow functions and scope ==
== Arrow functions and scope ==
Reference
* [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions Arrow functions]
* [https://www.codementor.io/dariogarciamoya/understanding-this-in-javascript-with-arrow-functions-gcpjwfyuc Understanding "this" in javascript with arrow functions]


<source lang="js">
<source lang="js">
Line 116: Line 123:
tahoe.print(); // Freel, Rose, Tallac, Rubicon, Silver
tahoe.print(); // Freel, Rose, Tallac, Rubicon, Silver
</source>
</source>


== Destructing objects ==
== Destructing objects ==
Line 259: Line 265:


== Spread operator ==
== Spread operator ==
Reference: [https://github.com/tc39/proposal-object-rest-spread Object Rest/Spread Properties for ECMAScript]


<source lang="js">
<source lang="js">
Line 327: Line 335:
// }
// }
</source>
</source>


== Asynchronous requests ==
== Asynchronous requests ==
Line 796: Line 803:
// {name: "Frederick Douglass", canRead: false, canWrite: false}
// {name: "Frederick Douglass", canRead: false, canWrite: false}
</source>
</source>
an impure function --it changes DOM
<source lang="js">
function Header(text) {
  let h1 = document.createElement("h1");
  h1.innerText = text;
  document.body.appendChild(h1);
}
Header("Header() caused side effects");
</source>
In React, UI is expressed with pure functions. e.g.
<source lang="js">
const Header = props => <h1>{props.title}</h1>;
</source>
==== Guideline for writing pure functions ====
# at least one argument
# return a value or another function
# should not change or mutate any of its arguments
=== Data Transformations ===
via Array.map and Array.reduce
using Array.join
<source lang="js">
const schools = ["Yorktown", "Washington & Lee", "Wakefield"];
console.log(schools.join(", "));
// "Yorktown, Washington & Lee, Wakefield"
</source>
create a new array of the schools that begin with the letter "W"
<source lang="js">
const wSchools = schools.filter(school => school[0] === "W");
console.log(wSchools);
// ["Washington & Lee", "Wakefield"]
</source>
when removing an item from an array, use Array.filter over .pop() or .splice() because .filter() is immutable
<source lang="js">
const cutSchool = (cut, list) => list.filter(school => school !== cut);
console.log(cutSchool("Washington & Lee", schools).join(", "));
// "Yorktown, Wakefield"
console.log(schools.join("\n"));
// Yorktown
// Washington & Lee
// Wakefield
</source>
Array.map takes a function as its argument which will be invoked once for every item in the array, and whatever it returns will be added to the new array
<source lang="js">
const highSchools = schools.map(school => `${school} High School`);
console.log(highSchools.join("\n"));
// Yorktown High School
// Washington & Lee High School
// Wakefield High School
console.log(schools.join("\n"));
// Yorktown
// Washington & Lee
// Wakefield
</source>
e.g. return an object for every school
<source lang="js">
const highSchools = schools.map(school => ({ name: school }));
console.log(highSchools);
// [
// { name: "Yorktown" },
// { name: "Washington & Lee" },
// { name: "Wakefield" }
// ]
</source>
pure f(x) that changes one object in an array of objects
<source lang="js">
let schools = [
  { name: "Yorktown" },
  { name: "Stratford" },
  { name: "Washington & Lee" },
  { name: "Wakefield" }
];
const editName = (oldName, name, arr) =>
  arr.map(item => {
    if (item.name === oldName) {
      return {
        ...item,
        name
      };
    } else {
      return item;
    }
  });
let updatedSchools = editName("Stratford", "HB Woodlawn", schools);
console.log(updatedSchools[1]); // { name: "HB Woodlawn" }
console.log(schools[1]); // { name: "Stratford" }
// equivalent to
const editName = (oldName, name, arr) =>
  arr.map(item => (item.name === oldName ? { ...item, name } : item));
</source>
transform schools object into an array of schools:
<source lang="js">
const schools = {
  Yorktown: 10,
  "Washington & Lee": 2,
  Wakefield: 5
};
const schoolArray = Object.keys(schools).map(key => ({
  name: key,
  wins: schools[key]
}));
console.log(schoolArray);
// [
// {
// name: "Yorktown",
// wins: 10
// },
// {
// name: "Washington & Lee",
// wins: 2
// },
// {
// name: "Wakefield",
// wins: 5
// }
// ]
</source>
<code>reduce</code> and <code>reduceRight</code> are used to trasnform an array into any value, including a number, string, boolean, object, or even a function
maximum number in an array of numbers
<source lang="js">
const ages = [21, 18, 42, 40, 64, 63, 34];
const maxAge = ages.reduce((max, age) => {
  console.log(`${age} > ${max} = ${age > max}`);
  if (age > max) {
    return age;
  } else {
    return max;
  }
}, 0);
console.log("maxAge", maxAge);
// 21 > 0 = true
// 18 > 21 = false
// 42 > 21 = true
// 40 > 42 = false
// 64 > 42 = true
// 63 > 64 = false
// 34 > 64 = false
// maxAge 64
// equivalent to
const max = ages.reduce((max, value) => (value > max ? value : max), 0);
</source>
reduce takes two arguments: a callback function & an original value
reduceRight simply starts reducing from the end of the array rather than the beginning
transform an array into an object
<source lang="js">
const colors = [
  {
    id: "xekare",
    title: "rad red",
    rating: 3
  },
  {
    id: "jbwsof",
    title: "big blue",
    rating: 2
  },
  {
    id: "prigbj",
    title: "grizzly grey",
    rating: 5
  },
  {
    id: "ryhbhsl",
    title: "banana",
    rating: 1
  }
];
const hashColors = colors.reduce((hash, { id, title, rating }) => {
  hash[id] = { title, rating };
  return hash;
}, {});
console.log(hashColors);
// {
// "xekare": {
// title:"rad red",
// rating:3
// },
// "jbwsof": {
// title:"big blue",
// rating:2
// },
// "prigbj": {
// title:"grizzly grey",
// rating:5
// },
// "ryhbhsl": {
// title:"banana",
// rating:1
// }
// }
</source>
reducing an array with multiple instances of the same value to an array of unique values
<source lang="js">
const colors = ["red", "red", "green", "blue", "green"];
const uniqueColors = colors.reduce(
  (unique, color) =>
    unique.indexOf(color) !== -1 ? unique : [...unique, color],
  []
);
console.log(uniqueColors);
// ["red", "green", "blue"]
</source>
=== Higher-Order Functions ===
functions that can manipulate other functions; can take functions in as arguments, or return functions, or both
e.g.
<source lang="js">
const invokeIf = (condition, fnTrue, fnFalse) =>
  condition ? fnTrue() : fnFalse();
const showWelcome = () => console.log("Welcome!!!");
const showUnauthorized = () => console.log("Unauthorized!!!");
invokeIf(true, showWelcome, showUnauthorized); // "Welcome!!!"
invokeIf(false, showWelcome, showUnauthorized); // "Unauthorized!!!"
</source>
e.g. currying
<source lang="js">
const userLogs = userName => message =>
  console.log(`${userName} -> ${message}`);
const log = userLogs("grandpa23");
log("attempted to load 20 fake members");
getFakeMembers(20).then(
  members => log(`successfully loaded ${members.length} members`),
  error => log("encountered an error loading members")
);
// grandpa23 -> attempted to load 20 fake members
// grandpa23 -> successfully loaded 20 members
// grandpa23 -> attempted to load 20 fake members
// grandpa23 -> encountered an error loading members
</source>
=== Recursion ===
<source lang="js">
const countdown = (value, fn) => {
  fn(value);
  return value > 0 ? countdown(value - 1, fn) : value;
};
countdown(10, value => console.log(value));
// 10
// 9
// 8
// 7
// 6
// 5
// 4
// 3
// 2
// 1
// 0
</source>
recursion is well-suited for searching through data structures
<source lang="js">
const dan = {
  type: "person",
  data: {
    gender: "male",
    info: {
      id: 22,
      fullname: {
        first: "Dan",
        last: "Deacon"
      }
    }
  }
};
const deepPick = (fields, object = {}) => {
  const [first, ...remaining] = fields.split(".");
  return remaining.length
    ? deepPick(remaining.join("."), object[first])
    : object[first];
};
deepPick("type", dan); // "person"
deepPick("data.info.fullname.first", dan); // "Dan"
deepPick("data.info.fullname.first", dan); // "Deacon"
// First Iteration
// first = "data"
// remaining.join(".") = "info.fullname.first"
// object[first] = { gender: "male", {info} }
// Second Iteration
// first = "info"
// remaining.join(".") = "fullname.first"
// object[first] = {id: 22, {fullname}}
// Third Iteration
// first = "fullname"
// remaining.join("." = "first"
// object[first] = {first: "Dan", last: "Deacon" }
// Finally...
// first = "first"
// remaining.length = 0
// object[first] = "Deacon"
</source>
=== Composition ===
chaining
<source lang="js">
const template = "hh:mm:ss tt";
const clockTime = template
  .replace("hh", "03")
  .replace("mm", "33")
  .replace("ss", "33")
  .replace("tt", "PM");
console.log(clockTime);
// "03:33:33 PM"
</source>
<code>both</code> function pipes a value through two separate functions.
<source lang="js">
const both = date => appendAMPM(civilianHours(date));
// but hard to read, so better approach is to use higher order function
const compose = (...fns) => arg =>
  fns.reduce((composed, f) => f(composed), arg);
const both = compose(
  civilianHours,
  appendAMPM
);
both(new Date());
</source>
== Putting it all together ==
ticking time
<source lang="js">
// Log Clock Time every Second
setInterval(logClockTime, 1000);
function logClockTime() {
  // Get Time string as civilian time
  let time = getClockTime();
  // Clear the Console and log the time
  console.clear();
  console.log(time);
}
function getClockTime() {
  // Get the Current Time
  let date = new Date();
  let time = "";
  // Serialize clock time
  let time = {
    hours: date.getHours(),
    minutes: date.getMinutes(),
    seconds: date.getSeconds(),
    ampm: "AM"
  };
  // Convert to civilian time
  if (time.hours == 12) {
    time.ampm = "PM";
  } else if (time.hours > 12) {
    time.ampm = "PM";
    time.hours -= 12;
  }
  // Prepend a 0 on the hours to make double digits
  if (time.hours < 10) {
    time.hours = "0" + time.hours;
  }
  // prepend a 0 on the minutes to make double digits
  if (time.minutes < 10) {
    time.minutes = "0" + time.minutes;
  }
  // prepend a 0 on the seconds to make double digits
  if (time.seconds < 10) {
    time.seconds = "0" + time.seconds;
  }
  // Format the clock time as a string "hh:mm:ss tt"
  return time.hours + ":" + time.minutes + ":" + time.seconds + " " + time.ampm;
}
</source>
REFACTORING using what we learned
in functional programs, use functions over values wherever possible; invoke the function to obtain the value when needed
<source lang="js">
const oneSecond = () => 1000;
const getCurrentTime = () => new Date();
const clear = () => console.clear();
const log = message => console.log(message);
</source>
three functions will be used to mutate the clock
# serializeClockTime - take a date object and returns a object for clock time that contains hours minutes, and seconds.
# civilianHours - takes the clock time object and returns an object where hours are converted to civilian time (1300 becomes 1:00)
# appendAMPM - take the clock time object and appends time of day, AM or PM, to that object.
<source lang="js">
const serializeClockTime = date => ({
  hours: date.getHours(),
  minutes: date.getMinutes(),
  seconds: date.getSeconds()
});
const civilianHours = clockTime => ({
  ...clockTime,
  hours: clockTime.hours > 12 ? clockTime.hours - 12 : clockTime.hours
});
const appendAMPM = clockTime => ({
  ...clockTime,
  ampm: clockTime.hours >= 12 ? "PM" : "AM"
});
</source>
higher order functions needed
# display - takes a target function and returns a function that will send a time to the target. In this eample the target will be console.log
# formatClock - takes a template string and uses it to return clock time formatted based upon the criteria from the string.
# prependZero -
<source lang="js">
const display = target => time => target(time);
const formatClock = format => time =>
  format
    .replace("hh", time.hours)
    .replace("mm", time.minutes)
    .replace("ss", time.seconds)
    .replace("tt", time.ampm);
const prependZero = key => clockTime => ({
  ...clockTime,
  [key]: clockTime[key] < 10 ? "0" + clockTime[key] : clockTime[key]
});
</source>
compose
<source lang="js">
const convertToCivilianTime = clockTime =>
  compose(
    appendAMPM,
    civilianHours
  )(clockTime);
const doubleDigits = civilianTime =>
  compose(
    prependZero("hours"),
    prependZero("minutes"),
    prependZero("seconds")
  )(civilianTime);
const startTicking = () =>
  setInterval(
    compose(
      clear,
      getCurrentTime,
      serializeClockTime,
      convertToCivilianTime,
      doubleDigits,
      formatClock("hh:mm:ss tt"),
      display(log)
    ),
    oneSecond()
  );
startTicking();
</source>
= How React Works =
== React elements ==
<source lang="js">
React.createElement("h1", { id: "recipe-0" }, "Baked Salmon");
// <h1 id="recipe-0">Baked Salmon</h1>
// log:
{
  $$typeof: Symbol(React.element),
  "type": "h1",
  "key": null,
  "ref": null,
  "props": {id: "recipe-0", children: "Baked Salmon"},
  "_owner": null,
  "_store": {}
}
</source>
== ReactDOM ==
contains tools necessary to render React element in the browser via '''render''' method
<source lang="js">
const dish = React.createElement("h1", null, "Baked Salmon");
ReactDOM.render(dish, document.getElementById("root"));
</source>
rendering array of elements
<source lang="js">
const dish = React.createElement("h1", null, "Baked Salmon");
const dessert = React.createElement("h2", null, "Coconut Cream Pie");
ReactDOM.render([dish, dessert], document.getElementById("root"));
</source>
== Children ==
<source lang="js">
React.createElement(
  "ul",
  null,
  React.createElement("li", null, "2 lb salmon"),
  React.createElement("li", null, "5 sprigs fresh rosemary"),
  React.createElement("li", null, "2 tablespoons olive oil"),
  React.createElement("li", null, "2 small lemons"),
  React.createElement("li", null, "1 teaspoon kosher salt"),
  React.createElement("li", null, "4 cloves of chopped garlic")
);
// equivalent to
const items = [
  "2 lb salmon",
  "5 sprigs fresh rosemary",
  "2 tablespoons olive oil",
  "2 small lemons",
  "1 teaspoon kosher salt",
  "4 cloves of chopped garlic"
];
React.createElement(
  "ul",
  { className: "ingredients" },
  items.map((ingredient, i) => React.createElement("li", { key: i }, ingredient))
);
</source>
== React Components ==
<source lang="js">
function IngredientsList({ items }) { // destructure items from props
  return React.createElement(
    "ul",
    { className: "ingredients" },
    items.map((ingredient, i) => React.createElement("li", { key: i }, ingredient)
  );
}
const items = [
  "2 lb salmon",
  "5 sprigs fresh rosemary",
  "2 tablespoons olive oil",
  "2 small lemons",
  "1 teaspoon kosher salt",
  "4 cloves of chopped garlic"
];
ReactDOM.render(
  React.createElement(IngredientsList, { items }, null),
  document.getElementById("root")
);
</source>
use functions to create components because class syntax is being deprecated.
= React with JSX =
== React elements as JSX ==
=== Nested components ===
<source lang="html">
<IngredientsList>
  <Ingredient />
  <Ingredient />
  <Ingredient />
</IngredientsList>
</source>
=== ClassName ===
Since <code>class</code> is a reserved word in JavaScript, className is used to define the class attribute.
=== JavaScript Expressions ===
<source lang="js">
<h1>{title}</h1>
<input type="checkbox" defaultChecked="{false}" />
</source>
=== Evaluation ===
<source lang="js">
<h1>{"Hello" + title}</h1>
<h1>{title.toLowerCase().replace}</h1>
function appendTitle({ title }) {
  console.log(`${title} is great!`);
}
</source>
=== Mapping Arrays with JSX ===
<source lang="js">
<ul>
  {props.ingredients.map((ingredient, i) => (
    <li key="{i}">{ingredient}</li>
  ))}
</ul>
</source>
== Babel ==
template file to use
<source lang="html">
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>React Examples</title>
  </head>
  <body>
    <div id="root"></div>
    <!-- React Library & React DOM -->
    <script src="https://unpkg.com/react@16.8.6/umd/react.development.js"></script>
    <script src="https://unpkg.com/react-dom@16.8.6/umd/react-dom.development.js"></script>
    <script src="https://unpkg.com/@babel/standalone/babel.min.js"></script>
    <script type="text/babel">
      // JSX code here. Or link to separate JavaScript file that contains JSX.
    </script>
  </body>
</html>
</source>
== Recipes as JSX ==
<source lang="js">
const data = [
  {
    name: "Baked Salmon",
    ingredients: [
      { name: "Salmon", amount: 1, measurement: "l lb" },
      { name: "Pine Nuts", amount: 1, measurement: "cup" },
      { name: "Butter Lettuce", amount: 2, measurement: "cups" },
      { name: "Yellow Squash", amount: 1, measurement: "med" },
      { name: "Olive Oil", amount: 0.5, measurement: "cup" },
      { name: "Garlic", amount: 3, measurement: "cloves" }
    ],
    steps: [
      "Preheat the oven to 350 degrees.",
      "Spread the olive oil around a glass baking dish.",
      "Add the yellow squash and place in the oven for 30 mins.",
      "Add the salmon, garlic, and pine nuts to the dish.",
      "Bake for 15 minutes.",
      "Remove from oven. Add the lettuce and serve."
    ]
  },
  {
    name: "Fish Tacos",
    ingredients: [
      { name: "Whitefish", amount: 1, measurement: "l lb" },
      { name: "Cheese", amount: 1, measurement: "cup" },
      { name: "Iceberg Lettuce", amount: 2, measurement: "cups" },
      { name: "Tomatoes", amount: 2, measurement: "large" },
      { name: "Tortillas", amount: 3, measurement: "med" }
    ],
    steps: [
      "Cook the fish on the grill until cooked through.",
      "Place the fish on the 3 tortillas.",
      "Top them with lettuce, tomatoes, and cheese."
    ]
  }
];
// A function component for an individual Recipe
function Recipe (props) {
  ...
}
// A function component for the Menu of Recipes
function Menu (props) {
  return (
    <article>
      <header>
        <h1>{props.title}</h1>
      </header>
<div className="recipes">
  {props.recipes.map((recipe, i) => (
    <Recipe
      key={i}
      name={recipe.name}
      ingredients={recipe.ingredients}
      steps={recipe.steps}
    />
  ))}
// equivalent to
{
  props.recipes.map((recipe, i) => <Recipe key={i} {...recipe} />);
}
</div>
    </article>
  );
}
// A call to ReactDOM.render to render our Menu into the current DOM
ReactDOM.render(
  <Menu recipes={data} title="Delicious Recipes" />,
  document.getElementById("root")
);
</source>
we can access title & recipes vars directly, so vars don't have to be prefixed with props:
<source lang="js">
function Menu({ title, recipes }) {
  return (
    <article>
      <header>
        <h1>{title}</h1>
      </header>
      <div className="recipes">
        {recipes.map((recipe, i) => (
          <Recipe key={i} {...recipe} />
        ))}
      </div>
    </article>
  );
}
</source>
code for the component for each individual recipe:
<source lang="js">
function Recipe({ name, ingredients, steps }) {
  return (
    <section id={name.toLowerCase().replace(/ /g, "-")}>
      <h1>{name}</h1>
      <ul className="ingredients">
        {ingredients.map((ingredient, i) => (
          <li key={i}>{ingredient.name}</li>
        ))}
      </ul>
      <section className="instructions">
        <h2>Cooking Instructions</h2>
        {steps.map((step, i) => (
          <p key={i}>{step}</p>
        ))}
      </section>
    </section>
  );
}
</source>
== React fragments ==
<source lang="js">
function Cat({ name }) {
  return (
    <React.Fragment>
      <h1>The cat's name is {name}</h1>
      <p>He's good.</p>
    </React.Fragment>
  );
}
// equivalent to
function Cat({ name }) {
  return (
    <>
      <h1>The cat's name is {name}</h1>
      <p>He's good.</p>
    </>
  );
}
</source>
== Intro to webpack ==
* Code splitting
* Minification
* Feature flagging
* Hot module replacement (HMR)
* Modularity
* Composition
* Speed
* Consistency
Installing webpack
<source lang="console">
$ npm install --save-dev webpack@next webpack-cli
</source>
Installing Babel dependencies
<source lang="console">
$ npm install babel-loader @babel/core --save-dev
</source>
Specify Babel presets
<source lang="console">
$ npm install @babel/preset-env @babel/preset-react --save-dev
</source>
= React State Management =
= Reference =
* [https://react-icons.netlify.com React Icons]
* Personal blogs
** [https://www.leighhalliday.com Leigh Halliday]
** [https://www.robinwieruch.de Robin Wieruch]
Retrieved from "https://wiki.michaelhan.net/Special:MobileDiff/3153...3184"