Object(JavaScript)

宣告

{鍵 (Key) : 值 (Value)}

new Object()

資料或函式的組合＝Property

透過.Key或['Key']存取或操作Object裡的property

obj[key] = value

刪除使用delete

delete obj[key]

一些原始資料型別、特殊資料型別也是Object

Boolean、Number、String、Array、Date、Function、RegExp

code:javascript

{ key: value }

!("key" in obj)

Object.assign()

Object.create()

Object.entries()

以[key, value]的形式回傳陣列

Object.fromEntries()

將陣列轉換為Object

刪除重複元素

Object.fromEntries(new Map(Object.entries(obj_with_duplicated_key)))

轉為Map後再轉回

Object.hasOwn()

Object.prototype.hasOwnProperty()

Object.is()

Object.keys()

Object.prototype.toLocaleString()

Object.prototype.toString()

Object.prototype.valueOf()

Object.values()

複製

code:javascript

// Shallow Copy

// only copy first depth data

const shallowCopy = { ...obj };

// Deep Copy

// use JSON.parse/stringify

const deepCopy = JSON.parse(JSON.stringify(obj));

// or use loadsh

const deepCopy = _.cloneDeep(obj);

How to Check If an Object Has a Property in JavaScript | Built In

Object內的資料順序

Map - JavaScript | MDN

Although the keys of an ordinary Object are ordered now, this was not always the case, and the order is complex. As a result, it's best not to rely on property order.

The order was first defined for own properties only in ECMAScript 2015; ECMAScript 2020 defines order for inherited properties as well. But note that no single mechanism iterates all of an object's properties; the various mechanisms each include different subsets of properties. (for-in includes only enumerable string-keyed properties; Object.keys includes only own, enumerable, string-keyed properties; Object.getOwnPropertyNames includes own, string-keyed properties even if non-enumerable; Object.getOwnPropertySymbols does the same for just Symbol-keyed properties, etc.)

javascript - Show original order of object properties in console.log - Stack Overflow

javascript - Does ES6 introduce a well-defined order of enumeration for object properties? - Stack Overflow