[JS] Object

An Object is logically a collection of properties.

Properties are identified using key values. A property key value is either an ECMAScript String value or a Symbol value. All String and Symbol values, including the empty String, are valid as property keys. A property name is a property key that is a String value.

Property keys are used to access properties and their values(p.89)

• 物件是由許多 屬性(properties) 所組成
• 物件的屬性也就是所謂的 key，使用 key 來取得物件的屬性和對應的值
• key 一定要是 string 或 symbol；即使是空字串也可以拿來當作 key

var user = {
    name: 'John',
    age: 18,
    hobby: 'soccer',
    isMarried: false,
    spells: ['shazam', 'abrakadra', 'boo'],
    shout: function () {
        console.log('AHHHHH!');
    },
};

console.log(user.name); // John
console.log(user[age]); // 18

取得物件的屬性與值

使用 obj.key 或 obj['key'] 來獲取物件的屬性與值。

刪除物件的屬性與值

使用 delete 運算子移除物件的屬性：delete obj.key，其返回值在大多數情況下皆為 true。

let obj = {
    name: 'John',
    age: 18,
};

delete obj.name; // true
delete obj.hobby; // true

console.log(obj); // {age: 18}