React: Difference between revisions
Line 300: | Line 300: | ||
directions("Truckee", "Tahoe City", "Sunnyside", "Homewood", "Tahoma"); | directions("Truckee", "Tahoe City", "Sunnyside", "Homewood", "Tahoma"); | ||
</source> | |||
combining objects: | |||
<source lang="js"> | |||
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" | |||
// } | |||
</source> | </source> |
Revision as of 23:51, 30 September 2019
Installation
// initialize a nodejs project (creates package.json)
$ npm init -y
// package manager
$ npm install yarn
$ yarn install packagename
$ yarn remove packagename
JavaScript
Three ways to declare variables are
- const
- var
- 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"
// }