[js] Object Method

這些 method 存在於 Object 的 Prototype 之中，只列出遇過的，可能會慢慢補上。

static: The static keyword defines a static method or field for a class, or a static initialization block (see the link for more information about this usage). Static properties cannot be directly accessed on instances of the class. Instead, they're accessed on the class itself.

Object.create()

(static method)

const pro = {
  name: "default",
};
 
// 以pro當作prototype生成一個新object
const a = Object.create(pro);
 
console.log(a);
// Expected output: {}
 
console.log(a.name);
// Expected output: "default"

Object.hasOwnProperty()

const pro = {
  name: "default",
};
 
const a = Object.create(pro);
 
a.color = "red";
 
console.log(a.hasOwnProperty("name"));
// name 存在於 prototype 不是自己的
// Expected output: false
 
console.log(a.hasOwnProperty("color"));
// Expected output: true

Object.keys(), Object.values()

(static method)

會回傳含有所有 key 或 value 的 array，很常見會拿來做 mapping 或是 foreach。

const object1 = {
  a: "somestring",
  b: 42,
  c: false,
  d: 42,
};
 
console.log(Object.keys(object1));
// Expected output: ["a", "b", "c", "d"]
 
console.log(Object.values(object1));
// Expected output: ["somestring", 42, false, 42]

Object.assign()

(static method)

const target = { a: 1, b: 2 };
const source = { b: 4, c: 5 };
 
const returnedTarget = Object.assign(target, source);
 
console.log(target);
// Expected output: Object { a: 1, b: 4, c: 5 }
 
console.log(returnedTarget === target);
// Expected output: true
// 回傳的結果是變動後的target object