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entries()

entries() 方法返回一个新的Array Iterator对象，该对象包含数组中每个索引的键/值对。

Try it​

const array1 = ["a", "b", "c"];

const iterator1 = array1.entries();

console.log(iterator1.next().value);
// expected output: Array [0, "a"]

console.log(iterator1.next().value);
// expected output: Array [1, "b"]

语法​

arr.entries()

返回值 一个新的 Array 迭代器对象。Array Iterator 是对象，它的原型（proto:Array Iterator）上有一个 next 方法，可用用于遍历迭代器取得原数组的 [key,value]。

Example​

iterator.next 方法运行​

var arr = ["a", "b", "c"];
var iter = arr.entries();
var a = [];

// for(var i=0; i< arr.length; i++){   // 实际使用的是这个
for (var i = 0; i < arr.length + 1; i++) {
  // 注意，是 length+1，比数组的长度大
  var tem = iter.next(); // 每次迭代时更新 next
  console.log(tem.done); // 这里可以看到更新后的 done 都是 false
  if (tem.done !== true) {
    // 遍历迭代器结束 done 才是 true
    console.log(tem.value);
    a[i] = tem.value;
  }
}

console.log(a); // 遍历完毕，输出 next.value 的数组

二维数组按行排序​

function sortArr(arr) {
  var goNext = true;
  var entries = arr.entries();
  while (goNext) {
    var result = entries.next();
    if (result.done !== true) {
      result.value[1].sort((a, b) => a - b);
      goNext = true;
    } else {
      goNext = false;
    }
  }
  return arr;
}

var arr = [
  [1, 34],
  [456, 2, 3, 44, 234],
  [4567, 1, 4, 5, 6],
  [34, 78, 23, 1],
];
sortArr(arr);

/*(4) [Array(2), Array(5), Array(5), Array(4)]
    0:(2) [1, 34]
    1:(5) [2, 3, 44, 234, 456]
    2:(5) [1, 4, 5, 6, 4567]
    3:(4) [1, 23, 34, 78]
    length:4
    __proto__:Array(0)
*/

使用 for…of 循环​

var arr = ["a", "b", "c"];
var iterator = arr.entries();
// undefined

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

// [0, "a"]
// [1, "b"]
// [2, "c"]

fromEntries​

format url​

const str = "age=zhoujielun&&name=16";
const ar = new URLSearchParams(str);
console.log(Object.fromEntries(ar));
//{age: "zhoujielun", name: "16"}

将对象中的属性数值统一*n​

const obj1 = { a: 1, b: 2, c: 3, d: "isD" };
const obj2 = Object.fromEntries(
  Object.entries(obj1).map(([key, val]) => {
    if (typeof val === "number") return [key, val * 2];
    else return [key, val];
  })
);
console.log(obj2);
//{a: 2, b: 4, c: 6, d: "isD"}

转化 array​

const arr = [
  ["0", "a"],
  ["1", "b"],
  ["2", "c"],
];
console.log(Object.fromEntries(arr));
// {0: "a", 1: "b", 2: "c"}

转化 map​

const map = new Map([
  ["name", "周杰伦"],
  ["age", 36],
]);

console.log(Object.fromEntries(map));
// {name: "周杰伦", age: 36}

参考​