如何在javascript中迭代（键，值）？ [英] How to iterate (keys, values) in javascript?

问题描述

我的字典格式为

dictionary = {0: {object}, 1:{object}, 2:{object}}

如何通过执行类似

How can I iterate through this dictionary by doing something like

for((key,value) in dictionary){
  //Do stuff where key would be 0 and value would be the object
}

推荐答案

tl;博士

1. 在ECMAScript 5中，它是不可能的。


2. 在ECMAScript 2015中，可以使用 Map s。


3. 在ECMAScript 2017中，它随时可用。

1. In ECMAScript 5, it is not possible.
2. In ECMAScript 2015, it is possible with Maps.
3. In ECMAScript 2017, it would be readily available.

ECMAScript 5：

不，对象无法实现。

您应该使用 for..in ，或 Object.keys ，像这样

You should either iterate with for..in, or Object.keys, like this

for (var key in dictionary) {
    // check if the property/key is defined in the object itself, not in parent
    if (dictionary.hasOwnProperty(key)) {           
        console.log(key, dictionary[key]);
    }
}

注意： 如果上面的条件是必要的，只有当你想要迭代属于 dictionary 对象的属性时。因为 for..in 将遍历所有继承的可枚举属性。

Note: The if condition above is necessary, only if you want to iterate the properties which are dictionary object's very own. Because for..in will iterate through all the inherited enumerable properties.

或

Object.keys(dictionary).forEach(function(key) {
    console.log(key, dictionary[key]);
});

---

ECMAScript 2015

在ECMAScript 2015中，您可以使用 Map 对象并使用 Map.prototype.entries 。从该页面引用示例，

In ECMAScript 2015, you can use Map objects and iterate them with Map.prototype.entries. Quoting example from that page,

var myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

var mapIter = myMap.entries();

console.log(mapIter.next().value); // ["0", "foo"]
console.log(mapIter.next().value); // [1, "bar"]
console.log(mapIter.next().value); // [Object, "baz"]

或者用 for..of ，像这样

Or iterate with for..of, like this

'use strict';

var myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

for (const entry of myMap.entries()) {
  console.log(entry);
}

输出

[ '0', 'foo' ]
[ 1, 'bar' ]
[ {}, 'baz' ]

或

for (const [key, value] of myMap.entries()) {
  console.log(key, value);
}

输出

0 foo
1 bar
{} baz

---

ECMAScript 2017

ECMAScript 2017将引入一个新功能 Object.entries 。您可以使用它来根据需要迭代对象。

ECMAScript 2017 would introduce a new function Object.entries. You can use this to iterate the object as you wanted.

'use strict';

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

输出

a 1
b 2
c 3

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