JavaScript 对象迭代方法与性能比较 • Usubeni Fantasy

原文地址：Iterating Over JavaScript Object Entries and their Performance - 5 Techniques

Object.entries

返回对象所有可枚举的键值对，不会追寻原型链上的 key

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3",
};

Object.entries(obj).forEach((entry) => {
  let key = entry[0];
  let value = entry[1];
  // entry 会是这样 ["key1", "value1"]
});

Object.keys

返回对象所有可枚举的键

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3",
};

Object.keys(obj).forEach((key) => {
  let value = obj[key];
});

Object.values

返回对象所有可枚举的值

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3",
};

Object.values(obj).forEach((value) => {
  // 只能使用 value
});

for…in loop

迭代可枚举属性，会顺着原型链找下去

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3",
};

for (const key in obj) {
  let value = obj[key];

  if (obj.hasOwnProperty(key)) {
    // 本身的
  } else {
    // 来自原型链的
  }
}

Object.getOwnPropertyNames

返回对象所有（包括不可枚举）的键（原文说会找原型链是错的）

let obj = {
  key1: "value1",
  key2: "value2",
  key3: "value3",
};

Object.getOwnPropertyNames(obj).forEach((key) => {
  let value = obj[key];
});

性能比较

下面的代码用上面的几种方法遍历有 1000000 个属性的对象，循环 10 次

const { PerformanceObserver, performance } = require("perf_hooks");

let objectSize = 1000000;
let iterations = 10;

console.log(
  "Starting performance test with %d object size and %d iterations",
  objectSize,
  iterations,
);

let values = {
  ENTRIES: 0,
  KEYS: 0,
  VALUES: 0,
  FORIN: 0,
  GETOWP: 0,
};

const obs = new PerformanceObserver((items) => {
  let entry = items.getEntries()[0];
  console.log(entry.name, entry.duration);
  values[entry.name] += entry.duration;
  performance.clearMarks();
});
obs.observe({ entryTypes: ["measure"] });

function generateObject() {
  let obj = {};
  for (let i = 0; i < objectSize; i++) {
    obj["key" + Math.random()] = "val" + Math.random();
  }
  return obj;
}

for (let i = 0; i < iterations; i++) {
  let obj = generateObject();

  //Object.entries
  performance.mark("A");
  Object.entries(obj).forEach((entry) => {
    let key = entry[0];
    let value = entry[1];
  });
  performance.mark("B");
  performance.measure("ENTRIES", "A", "B");

  //Object.Keys
  performance.mark("A");
  Object.keys(obj).forEach((key) => {
    let value = obj[key];
  });
  performance.mark("B");
  performance.measure("KEYS", "A", "B");

  //Object.Values
  performance.mark("A");
  Object.values(obj).forEach((value) => {});
  performance.mark("B");
  performance.measure("VALUES", "A", "B");

  //For In
  performance.mark("A");
  for (const key in obj) {
    let value = obj[key];
  }
  performance.mark("B");
  performance.measure("FORIN", "A", "B");

  //Object.getOwnPropertyNames
  performance.mark("A");
  Object.getOwnPropertyNames(obj).forEach((key) => {
    let value = obj[key];
  });
  performance.mark("B");
  performance.measure("GETOWP", "A", "B");
}

console.log(
  Object.entries(values).sort((a, b) => {
    return a[1] - b[1];
  }),
);

下面的结果是我自己跑的，顺序的是指赋值的时候直接用 index，随机则是键值对都插入随机数，得到的性能排序是和作者一样的，也因为 node.js 和 chrome 都是 V8，所以这个应该也是代表在浏览器上的性能排序。

// 顺序
[
  ["FORIN", 4677.321499],
  ["KEYS", 4812.776572],
  ["GETOWP", 8610.906197],
  ["VALUES", 9914.674390999999],
  ["ENTRIES", 19338.083694],
];

// 随机
[
  ["KEYS", 4502.579589],
  ["FORIN", 4678.013548000001],
  ["GETOWP", 8880.325031999999],
  ["VALUES", 10104.106962],
  ["ENTRIES", 17089.637588999998],
];

之前听说引擎会猜测下一个值让运行速度更快，看数据似乎没有太大影响。

也算是一点干货，快点来原文给作者鼓鼓掌吧 👏