[드림코딩][ES6] 자바스크립트 7. 오브젝트 넌 뭐니? | 프론트엔드 개발자 입문편

'use strict';
// Objects
// one of the JavaScript's data types.
// a collection of related data and/or functionality.
// Nearly all objects in JavaScript are instances of Object
// object = { key : value };
const obj1 = {}; // 'object literal' syntax
const obj2 = new Object(); // 'object constructor' syntax

function print(person) {
    console.log(person.name);
    console.log(person.age);
}

const ellie = {
    name: 'ellie',
    age: 4
};
print(ellie);

// with JavaScript magic (dynamically typed language)
// can add properties later
ellie.hasJob = true;
console.log(ellie.hasJob);

// can delete properties later
delete ellie.hasJob;
console.log(ellie.hasJob);

// 2. Computed properties
// key should be always string
console.log(ellie.name);
console.log(ellie['name']);
ellie['hasJob'] = true;
console.log(ellie.hasJob);

function printValue(obj, key) {
    console.log(obj[key]);
}
printValue(ellie, 'name');
printValue(ellie, 'age');

// 3. Property value shorthand
const person1 = {
    name: 'bob',
    age: 2
};
const person2 = {
    name: 'steve',
    age: 3
};
const person3 = {
    name: 'dave',
    age: 4
};
const person4 = new Person('elile', 30);
console.log(person4);

// 4. Constructor Function
function Person(name, age) {
    // this = {};
    this.name = name;
    this.age = age;
    // return this;
}

// 5. in operator: property existence check (key in obj)
console.log('name' in ellie);
console.log('age' in ellie);
console.log('random' in ellie);
console.log(ellie.random);
// 6. for..in vs for..of
// for (key in obj)
console.clear();
for (let key in ellie) {
    console.log(key);
}

// for (value of iterable)
const array = [1, 2, 4, 5];
for (let value of array) {
    console.log(value);
}

// 7. Fun cloning
// Object.assign(dest, [obj1, obj2, obj3...])
const user = {
    name: 'ellie',
    age: '20'
};
const user2 = user;
console.log(user);

// old way
const user3 = {};
for (let key in user) {
    user3[key] = user[key];
}
console.clear();
console.log(user3);

const user4 = Object.assign({}, user);
console.log(user4);

// another example
const fruit1 = {
    color: 'red'
};
const fruit2 = {
    color: 'blue',
    size: 'big'
};
const mixed = Object.assign({}, fruit1, fruit2);
console.log(mixed.color);
console.log(mixed.size);