For..In循环中的JavaScript - 键值对

本文翻译自：For..In loops in JavaScript - key value pairs

I was wondering if there's a way to do something like a PHP foreach loop in JavaScript. 我想知道是否有办法在JavaScript中执行类似PHP foreach循环的操作。 The functionality I'm looking for is something like this PHP Snippet: 我正在寻找的功能就像这个PHP代码片段：

foreach($data as $key => $value) { }

I was looking at the JS for..in loop, but there seems to be no way to specify the as . 我正在查看JS for..in循环，但似乎没有办法指定as 。 If I do this with a 'normal' for loop ( for(var i = 0; i < data.length; i++ ), is there a way to grab the key => value pairs? 如果我使用' for(var i = 0; i < data.length; i++循环（ for(var i = 0; i < data.length; i++ ）），有没有办法获取key => value对？

---

#1楼

参考：https://stackoom.com/question/UNwU/For-In循环中的JavaScript-键值对

---

#2楼

for (var key in myMap) {
    if (myMap.hasOwnProperty(key)) {
        console.log("key =" + key);
        console.log("value =" + myMap[key]);
    }
}

In javascript, every object has a bunch of built-in key-value pairs that have meta-information. 在javascript中，每个对象都有一堆具有元信息的内置键值对。 When you loop through all the key-value pairs for an object you're looping through them too. 循环遍历对象的所有键值对时，也会循环遍历它们。 The use of hasOwnProperty() filters these out. 使用hasOwnProperty（）过滤掉这些。

---

#3楼

ES6 will provide Map.prototype.forEach(callback) which can be used like this ES6将提供Map.prototype.forEach（回调），可以像这样使用

myMap.forEach(function(value, key, myMap) {
                        // Do something
                    });

---

#4楼

If you can use ES6 natively or with Babel (js compiler) then you could do the following: 如果您可以本机使用ES6或使用Babel （js编译器），那么您可以执行以下操作：

 const test = {a: 1, b: 2, c: 3}; for (const [key, value] of Object.entries(test)) { console.log(key, value); } 

Which will print out this output: 哪个会打印出这个输出：

a 1
b 2
c 3

The Object.entries() method returns an array of a given object's own enumerable property [key, value] pairs, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well) . Object.entries()方法返回给定对象自己的可枚举属性[key, value]对的数组，其顺序与for...in循环提供的顺序相同（不同之处在于for-in循环枚举原型链中的属性也是如此） 。

• Object.entries documentation Object.entries文档
• for...of documentation 为......文件
• Destructuring assignment documentation 解构分配文档
• Enumerability and ownership of properties documentation 属性文档的可插入性和所有权

Hope it helps! 希望能帮助到你！ =) =）

---

#5楼

let test = {a: 1, b: 2, c: 3};
Object.entries(test).forEach(([key, value]) => console.log(key, value))

// a 1
// b 2
// c 3

---

#6楼

If you are using Lodash , you can use _.forEach 如果您使用的是Lodash ，则可以使用_.forEach

_.forEach({ 'a': 1, 'b': 2 }, function(value, key) {
  console.log(key + ": " + value);
});
// => Logs 'a: 1' then 'b: 2' (iteration order is not guaranteed).