entries() for...in for...of

[5Mi]

//解构赋值   数组arr.entries()转化后返回每项为键值对的数组
for(let [index,charge] of this.charges.entries()){
    //chargesType数组中是否含有 partType 没有就添加
    if(this.chargesType.indexOf(charge.partType) == -1){
        this.chargesType.push(charge.partType);
    }
}

The entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.

数组entries()转化后返回一个Array Iterator对象,是一个每项为原素组键值对的数组 [index,value]

var arr = ['a', 'b', 'c'];
var eArr = arr.entries();

console.log(eArr.next().value); // [0, 'a']
console.log(eArr.next().value); // [1, 'b']
console.log(eArr.next().value); // [2, 'c']

Same as above, using a for…of loop:

var arr = ['a', 'b', 'c'];
var eArr = arr.entries();

for (let e of eArr) {
  console.log(e);
}

---

JavaScript原有的for...in循环，只能获得对象的键名，不能直接获取键值。ES6提供for...of循环，允许遍历获得键值。

var arr = ['a', 'b', 'c', 'd'];

for (let a in arr) {
  console.log(a); // 0 1 2 3
}

for (let a of arr) {
  console.log(a); // a b c d
}

上面代码表明，for...in循环读取键名，for...of循环读取键值。如果要通过for...of循环，获取数组的索引，可以借助数组实例的entries方法和keys方法，参见《数组的扩展》章节。

for...of循环调用遍历器接口，数组的遍历器接口只返回具有数字索引的属性。这一点跟for...in循环也不一样。

let arr = [3, 5, 7];
arr.foo = 'hello';

for (let i in arr) {
  console.log(i); // "0", "1", "2", "foo"
}

for (let i of arr) {
  console.log(i); //  "3", "5", "7"
}

上面代码中，for...of循环不会返回数组arr的foo属性。

[5Mi]

Object.entries(obj)

Object.entries() returns an array whose elements are arrays corresponding to the enumerable property [key, value] pairs found directly upon object. The ordering of the properties is the same as that given by looping over the property values of the object manually.

Examples

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

// array like object
var 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
var an_obj = { 100: 'a', 2: 'b', 7: 'c' };
console.log(Object.entries(an_obj)); // [ ['2', 'b'], ['7', 'c'], ['100', '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.entries(my_obj)); // [ ['foo', 'bar'] ]

// non-object argument will be coerced to an object
console.log(Object.entries("foo")); // [ ['0', 'f'], ['1', 'o'], ['2', 'o'] ]