Getting nested values in Immutable.js

问题

According to the docs here: 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 keyPath argument. This is what I've done, however I'm getting undefined as the return value.

http://jsfiddle.net/srxv4mwu/

var obj = Immutable.Map({categories: {1: 'a', 2: 'b'}});
var output = obj.getIn(['categories', 1]);
alert(output);

What am I doing wrong?

回答1:

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.

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 1 value, you can just do:

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 categories collection 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.

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'.

It would probably be more convenient for you to do something like below, if you have many nested maps.

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.

回答2:

There are 2 problems with your code:

Immutable.Map(...) doesn't traverse the parameter to create a complex immutable. For that you need Immutable.fromJS(...).
Once you do that, you need to use strings in getIn(...), so ['categories', '1'] instead of ['categories', 1].

See working fiddle.

来源：https://stackoverflow.com/questions/33910300/getting-nested-values-in-immutable-js

标签

javascript

immutable.js