[TIL] Modern JavaScript

矢印関数

const add = function (x, y) {
  return x + y;
}

const add = (x, y) => x + y;

const getStudentAvg = arr => {
  return arr
    .filter(person => person.job === 'student')
    .reduce((sum, person) => (sum + person.grade), 0);
}

Spread/Rest構文

let arrayToSpread = [1, 2];
add(...arrayToSpread); // 3

let arrayFromSpread = ...arrayToSpread;
console.log(arrayFromSpread); // [1, 2]

構造分解の割り当て

var o = {p: 42, q: true};
var {p, q} = o;

console.log(p); // 42
console.log(q); // true

function whois({displayName: displayName, fullName: {firstName: name}}){
  console.log(displayName + " is " + name);
}

let user = {
  id: 42,
  displayName: "jdoe",
  fullName: {
      firstName: "John",
      lastName: "Doe"
  }
};

whois(user); // "jdoe is John"

node.js

// script1.js
const module2 = require('./script2.js');
// script2.js
console.log('this is module 2');

// script1.js
const module2 = require('./script2.js')
console.log(modules2) // 'this is module 2'
// script2.js
module.exports = 'this is module 2'

module.exports.hello = true; // Exported from require of module
exports = { hello: false };  // Not exported, only available in the module

classes & instances

class Student {
  constructor(commitment, course, wave, name) {
    this.commitment = commitment;
    this.course = course;
    this.wave = wave;
    this.name = name;
  }
  
  getDisplayName () {
  	return `${this.commitment} ${this.course} ${this.wave} ${this.name}`;
  }
  
  printDisplayName () {
    console.log(this.getDisplayName());
  }
}

let me = new Student('Full', 'IM', '28', '도하영');
me.printDisplayName() // 'Full IM 28 도하영'

function methods