关于Object.entries()方法的使用和实现方式

Object.entries(obj)

const object = {
  a: 'string',
  b: 111,
  c: true,
  e: null,
  d: undefined,
  f: [3, 4, 5],
  g: { obj: '666' }
};

for (const [key, value] of Object.entries(object)) {
  console.log(`${key}: ${value}`);
}

// expected output:
// a: string
// b: 111
// c: true
// e: null
// d: undefined
// f: 3,4,5
// g: [object Object]

console.log(Object.entries(object));

// 正常对象枚举
const obj = { foo: 'bar', baz: 42 };
console.log(Object.entries(obj)); // [ ['foo', 'bar'], ['baz', 42] ]

// key为索引的对象
const obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.entries(obj)); // [ ['0', 'a'], ['1', 'b'], ['2', 'c'] ]

// key是数字类型，会按照从小到大枚举
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(anObj)); // [ ['2', 'b'], ['7', 'c'], ['100', 'a'] ]

// getFoo是不可枚举的属性
const myObj = Object.create({}, { getFoo: { value() { return this.foo; } } });
myObj.foo = 'bar';
console.log(Object.entries(myObj)); // [ ['foo', 'bar'] ]

// 非对象参数将被强制为对象
console.log(Object.entries('foo')); // [ ['0', 'f'], ['1', 'o'], ['2', 'o'] ]

// 通过 for...of 方式遍历键值
const obj = { a: 5, b: 7, c: 9 };
for (const [key, value] of Object.entries(obj)) {
	console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
}

// forEach 方法遍历
Object.entries(obj).forEach(([key, value]) => {
	console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
});

// 将 Object 转换为 Map
// new Map() 构造函数接受一个可迭代的entries。借助Object.entries方法你可以很容易的将Object转换为Map:
const obj = { foo: "bar", baz: 42 };
const map = new Map(Object.entries(obj));
console.log(map); // Map(2) { "foo" => "bar", "baz" => 42 }

// 将 Map 转换为 Object
const objByMap = Object.fromEntries(map);
console.log(objByMap); // { foo: 'bar', baz: 42 }

// 获取 url 传参
const str = "page=1&&row=10&&id=2&&name=test"
const params = new URLSearchParams(str)
console.log(Object.fromEntries(params)) // { page: '1', row: '10', id: '2', name: 'test' }

const entries = arg => {
  if (Array.isArray(arg)) return arg.map((x, index) => [`${index}`, x]);
  if (Object.prototype.toString.call(arg) === `[object Object]`) return Object.keys(arg).map(y => [y, arg[y]]);
  if (typeof arg === 'number') return [];
  throw '无法将参数转换为对象！'
}

// test Number
console.log(entries(1)); // []

// test Object
const obj = { foo: "bar", baz: 42 };
const map = new Map(entries(obj));
console.log(map); // Map(2) { "foo" => "bar", "baz" => 42 }

// test Array
const arr = [1, 2, 3];
console.log(entries(arr)); // [["0", 1], ["1", 2], ["2", 3]]

// test Error
console.log(entries('123')); // 无法将参数转换为对象！

const fromEntries = arg => {
  // Map
  if (Object.prototype.toString.call(arg) === '[object Map]') {
    const resMap = {};
    for (const key of arg.keys()) resMap[key] = arg.get(key);
    return resMap;
  }
  // Array
  if (Array.isArray(arg)) {
    const resArr = {}
    arg.map(([key, value]) => resArr[key] = value);
    return resArr
  }
  throw '参数不可编辑！';
}

// test Map
const map = new Map(Object.entries({ foo: "bar", baz: 42 }));
const obj = fromEntries(map);
console.log(obj); // { foo: 'bar', baz: 42 }

// test Array
const arr = [['0', 'a'], ['1', 'b'], ['2', 'c']];
const obj = fromEntries(arr);
console.log(obj); // { 0: 'a', 1: 'b', 2: 'c' }

// test Error
console.log(fromEntries(1)); // 参数不可编辑！

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

let {keys, values, entries} = Object;
let obj = { a: 1, b: 2, c: 3 };

for (let key of keys(obj)) {
  console.log(key); // 'a', 'b', 'c'
}

for (let value of values(obj)) {
  console.log(value); // 1, 2, 3
}

for (let [key, value] of entries(obj)) {
  console.log([key, value]); // ['a', 1], ['b', 2], ['c', 3]
}

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

const obj = { 100: 'a', 2: 'b', 7: 'c' };
Object.values(obj)
// ["b", "c", "a"]

const obj = Object.create({}, {p: {value: 42}});
Object.values(obj) // []

const obj = Object.create({}, {p:
  {
    value: 42,
    enumerable: true
  }
});
Object.values(obj) // [42]

Object.values({ [Symbol()]: 123, foo: 'abc' });
// ['abc']

Object.values('foo')
// ['f', 'o', 'o']

Object.values(42) // []
Object.values(true) // []

const obj = { foo: 'bar', baz: 42 };
Object.entries(obj)
// [ ["foo", "bar"], ["baz", 42] ]

Object.entries({ [Symbol()]: 123, foo: 'abc' });
// [ [ 'foo', 'abc' ] ]

let obj = { one: 1, two: 2 };
for (let [k, v] of Object.entries(obj)) {
  console.log(
    `${JSON.stringify(k)}: ${jsON.stringify(v)}`
  );
}
// "one": 1
// "two": 2

const obj = { foo: 'bar', baz: 42 };
const map = new Map(Object.entries(obj));
map // Map { foo: "bar", baz: 42 }

// Generator函数的版本
function* entries(obj) {
  for (let key of Object.keys(obj)) {
    yield [key, obj[key]];
  }
}

// 非Generator函数的版本
function entries(obj) {
  let arr = [];
  for (let key of Object.keys(obj)) {
    arr.push([key, obj[key]]);
  }
  return arr;
}