Object對象常用方法

Object.entries()方法返回一個給定對象自身可枚舉屬性的鍵值對數組，其排列與使用 for…in 循環遍歷該對象時返回的順序一致（區別在於 for-in 循環還會枚舉原型鏈中的屬性）。

const object3 = {
  a: 'somestring',
  b: 42
};

console.log(Object.entries(object3));//[[a: 'somestring'],[b: 42]]

for (let [key, value] of Object.entries(object3)) {
  console.log(`${key}: ${value}`);
}
// "a: somestring"
// "b: 42"

Object.fromEntries() 方法把鍵值對列表轉換爲一個對象。

const entries = new Map([
  ['foo', 'bar'],
  ['baz', 42]
]);

const obj = Object.fromEntries(entries);

console.log(obj);

// expected output: Object { foo: "bar", baz: 42 }

Object.assign() 方法用於將所有可枚舉屬性的值從一個或多個源對象複製到目標對象。它將返回目標對象。

const target = { a: 1, b: 2 };
const source = { b: 4, c: 5 };

const returnedTarget = Object.assign(target, source);//sourc複製到target對象，並與target對象和合並，然後返回target

console.log(target);
// expected output: Object { a: 1, b: 4, c: 5 }

console.log(returnedTarget);
// expected output: Object { a: 1, b: 4, c: 5 }

Object.keys() 方法會返回一個由一個給定對象的自身可枚舉屬性組成的數組，數組中屬性名的排列順序和使用 for…in 循環遍歷該對象時返回的順序一致 。

var arr = ['a', 'b', 'c'];
console.log(Object.keys(arr)); // console: ['0', '1', '2']

// array like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.keys(obj)); // console: ['0', '1', '2']

// array like object with random key ordering
var anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.keys(anObj)); // console: ['2', '7', '100']

// getFoo is a property which isn't enumerable
var myObj = Object.create({}, {
  getFoo: {
    value: function () { return this.foo; }
  } 
});
myObj.foo = 1;
console.log(Object.keys(myObj)); // console: ['foo']

Object.values()返回一個數組，其元素是在對象上找到的可枚舉屬性值。屬性的順序與通過手動循環對象的屬性值所給出的順序相同。

var obj = { foo: 'bar', baz: 42 };
console.log(Object.values(obj)); // ['bar', 42]

// array like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.values(obj)); // ['a', 'b', 'c']

// array like object with random key ordering
// when we use numeric keys, the value returned in a numerical order according to the keys
var an_obj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.values(an_obj)); // ['b', 'c', 'a']

// getFoo is property which isn't enumerable
var my_obj = Object.create({}, { getFoo: { value: function() { return this.foo; } } });
my_obj.foo = 'bar';
console.log(Object.values(my_obj)); // ['bar']

// non-object argument will be coerced to an object
console.log(Object.values('foo')); // ['f', 'o', 'o']