带你领略Object.assign()方法的操作方式

Object.assign(target, ...sources)

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);
// expected output: Object { a: 1, b: 4, c: 5 }

const target = { a: 1, b: 1 };
const source1 = { b: 2, c: 2 };
const source2 = { c: 3 };
Object.assign(target, source1, source2);
target // {a:1, b:2, c:3}

const obj = {a: 1};
Object.assign(obj) === obj // true

typeof Object.assign(2) // "object"

Object.assign(undefined) // 报错
Object.assign(null) // 报错

let obj = {a: 1};
Object.assign(obj, undefined) === obj // true
Object.assign(obj, null) === obj // true

const v1 = 'abc';
const v2 = true;
const v3 = 10;
const obj = Object.assign({}, v1, v2, v3);
console.log(obj); // { "0": "a", "1": "b", "2": "c" }

Object(true) // {[[PrimitiveValue]]: true}
Object(10)  //  {[[PrimitiveValue]]: 10}
Object('abc') // {0: "a", 1: "b", 2: "c", length: 3, [[PrimitiveValue]]: "abc"}

Object.assign({b: 'c'},
  Object.defineProperty({}, 'invisible', {
    enumerable: false,
    value: 'hello'
  })
)
// { b: 'c' }

Object.assign({ a: 'b' }, { [Symbol('c')]: 'd' })
// { a: 'b', Symbol(c): 'd' }

const obj1 = {a: {b: 1}};
const obj2 = Object.assign({}, obj1);
obj1.a.b = 2;
obj2.a.b // 2

const target = { a: { b: 'c', d: 'e' } }
const source = { a: { b: 'hello' } }
Object.assign(target, source)
// { a: { b: 'hello' } }

Object.assign([1, 2, 3], [4, 5])
// [4, 5, 3]

const source = {
  get foo() { return 1 }
};
const target = {};
Object.assign(target, source)
// { foo: 1 }

class Point {
  constructor(x, y) {
    Object.assign(this, {x, y});
  }
}

Object.assign(SomeClass.prototype, {
  someMethod(arg1, arg2) {
    ···
  },
  anotherMethod() {
    ···
  }
});
// 等同于下面的写法
SomeClass.prototype.someMethod = function (arg1, arg2) {
  ···
};
SomeClass.prototype.anotherMethod = function () {
  ···
};

function clone(origin) {
  return Object.assign({}, origin);
}

function clone(origin) {
  let originProto = Object.getPrototypeOf(origin);
  return Object.assign(Object.create(originProto), origin);
}

const merge = (target, ...sources) => Object.assign(target, ...sources);

const merge = (...sources) => Object.assign({}, ...sources);

const DEFAULTS = {
  logLevel: 0,
  outputFORMat: 'html'
};
function processContent(options) {
  options = Object.assign({}, DEFAULTS, options);
  console.log(options);
  // ...
}

const DEFAULTS = {
  url: {
    host: 'example.com',
    port: 7070
  },
};
processContent({ url: {port: 8000} })
// {
//   url: {port: 8000}
// }