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
推荐教程：《JS教程》
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