Javascript 在 Immutable.js 中获取嵌套值
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Getting nested values in Immutable.js
提问by xiankai
According to the docs here: https://facebook.github.io/immutable-js/docs/#/Map/getIn
根据这里的文档：https: //facebook.github.io/immutable-js/docs/#/Map/getIn
I should be able to get the deeply nested value by providing an array for the keyPathargument. This is what I've done, however I'm getting undefinedas the return value.
我应该能够通过为keyPath参数提供一个数组来获得深度嵌套的值。这就是我所做的，但是我得到的undefined是返回值。
var obj = Immutable.Map({categories: {1: 'a', 2: 'b'}});
var output = obj.getIn(['categories', 1]);
alert(output);
What am I doing wrong?
我究竟做错了什么？
回答by user1440308
A map is simply a collection of keys with values. What you have is a map with the key categories, and the value {1: 'a', 2: 'b'}. The value does not automatically become an Immutable map just because you place it inside another map.
映射只是具有值的键的集合。您拥有的是一个带有键categories和值的映射{1: 'a', 2: 'b'}。该值不会因为您将其放置在另一个地图中而自动成为不可变地图。
Now, the getIn()function will only "see" other Immutable.js maps. What you have in there is a regular ol' javascript object. If you just want to get the 1value, you can just do:
现在，该getIn()函数只会“看到”其他 Immutable.js 映射。你在那里有一个普通的 ol' javascript 对象。如果你只是想获得1价值，你可以这样做：
var obj = Immutable.Map({categories: {1: 'a', 2: 'b'}});
var output = obj.getIn(["categories"])[1];
alert(output);<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.1/immutable.min.js"></script>If you want the categoriescollection to also be a map, you'll have to define that explicitly. Also, as Amit pointed out, you'll need to use strings with the getIn()function.
如果您希望categories集合也成为地图，则必须明确定义它。此外，正如 Amit 指出的，您需要在getIn()函数中使用字符串。
var obj = Immutable.Map({
categories: Immutable.Map({
1: 'a',
2: 'b'
})
});
var output = obj.getIn(['categories', '1']);
alert(output);<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.1/immutable.min.js"></script>The above code will return 'a'.
上面的代码将返回'a'.
It would probably be more convenient for you to do something like below, if you have many nested maps.
如果您有许多嵌套地图，那么执行以下操作可能会更方便。
var obj = Immutable.fromJS({
categories: {
1: 'a',
2: 'b'
}
});
var output = obj.getIn(['categories', '1']);
alert(output);<script src="https://cdnjs.cloudflare.com/ajax/libs/immutable/3.8.1/immutable.min.js"></script>The fromJs()function will convert any nested objects into maps or lists automatically for you.
该fromJs()函数将自动为您将任何嵌套对象转换为地图或列表。
回答by Amit
There are 2 problems with your code:
您的代码有两个问题：
Immutable.Map(...)doesn't traverse the parameter to create a complex immutable. For that you needImmutable.fromJS(...).- Once you do that, you need to use strings in
getIn(...), so['categories', '1']instead of['categories', 1].
Immutable.Map(...)不遍历参数来创建一个复杂的不可变。为此，您需要Immutable.fromJS(...).- 一旦你这样做了，你需要在 中使用字符串
getIn(...)，['categories', '1']而不是['categories', 1].
See working fiddle.
请参阅工作小提琴。
