javascript 中Object.entries

参考：https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/entries

Object.entries()方法返回一个给定对象自身可枚举属性的键值对数组，其排列与使用 for...in 循环遍历该对象时返回的顺序一致（区别在于 for-in 循环还会枚举原型链中的属性）。

例子：

const log = console.log;function Animal(name) {this.name = name;
}Animal.prototype.run = function() {console.log(`${this.name} run`);
}function Cat(name) {Animal.call(this, name);this.age = 8;
}Cat.prototype = Object.create(Animal.prototype);
Cat.prototype.constructor = Cat;let c = new Cat("miao");
log("c = ", c);
for (let [k, v] of Object.entries(c)) { //不枚举原型中的属性log("entries k = ", k, ", v = ", v);
}for (let k in c) {log("in k = ", k, ", v = ", c[k]);
}
c.run();

结果：

$ node for.js
c =  Cat { name: 'miao', age: 8 }
entries k =  name , v =  miao
entries k =  age , v =  8
in k =  name , v =  miao
in k =  age , v =  8
in k =  constructor , v =  [Function: Cat]
in k =  run , v =  [Function]
miao run

例子：

const object1 = {a: 'somestring',b: 42
};for (const [key, value] of Object.entries(object1)) {console.log(`${key}: ${value}`);
}// expected output:
// "a: somestring"
// "b: 42"
// order is not guaranteed

语法

Object.entries(obj)

参数

obj

可以返回其可枚举属性的键值对的对象。

返回值

给定对象自身可枚举属性的键值对数组。

描述

Object.entries()返回一个数组，其元素是与直接在object上找到的可枚举属性键值对相对应的数组。属性的顺序与通过手动循环对象的属性值所给出的顺序相同。

示例

const obj = { foo: 'bar', baz: 42 };
console.log(Object.entries(obj)); // [ ['foo', 'bar'], ['baz', 42] ]// array like object
const obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.entries(obj)); // [ ['0', 'a'], ['1', 'b'], ['2', 'c'] ]// array like object with random key ordering
const anObj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(anObj)); // [ ['2', 'b'], ['7', 'c'], ['100', 'a'] ]// getFoo is property which isn't enumerable
const myObj = Object.create({}, { getFoo: { value() { return this.foo; } } });
myObj.foo = 'bar';
console.log(Object.entries(myObj)); // [ ['foo', 'bar'] ]// non-object argument will be coerced to an object
console.log(Object.entries('foo')); // [ ['0', 'f'], ['1', 'o'], ['2', 'o'] ]// iterate through key-value gracefully
const obj = { a: 5, b: 7, c: 9 };
for (const [key, value] of Object.entries(obj)) {console.log(`${key} ${value}`); // "a 5", "b 7", "c 9"
}// Or, using array extras
Object.entries(obj).forEach(([key, value]) => {
console.log(`${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:

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

Polyfill

要在较旧环境中添加兼容的Object.entries支持，你可以在 tc39/proposal-object-values-entries 中找到Object.entries的示例（如果你不需要任何对IE的支持），在 es-shims/Object.entries 资料库中的一个polyfill，或者你可以使用下面列出的简易 polyfill。

if (!Object.entries)Object.entries = function( obj ){var ownProps = Object.keys( obj ),i = ownProps.length,resArray = new Array(i); // preallocate the Arraywhile (i--)resArray[i] = [ownProps[i], obj[ownProps[i]]];return resArray;};

对于上述 polyfill 代码片段，如果你需要 IE9 以下的支持，那么你还需要一个 Object.keys polyfill（如 Object.keys页面上的）。