Immutable.js中的列表清单

Question

I want to have list of lists and push element to it, but I keep getting list with no elements and I can't think of the reason why.

I start with

List([ List([]), List([]) ]);

and I want to have

List([ List([2,4]), List([3,6]) ]);

The code I have is the following:

const { List } = require('immutable')

list = List([ List([]), List([]) ]);
list.get(0).push(2);
list.get(1).push(3);
list.get(0).push(4);
list.get(1).push(6);

console.log(list);

When I run it, it prints out:

List [ List [], List [] ]

There are no elements in the lists.

Answer 1

Of course there will be no elements in the List .

When you do

list.get(0).push(2);

You are not mutating the element at the position 0 by pushing 2 into it as you're assuming, you're getting a new List that is the result of doing that operation, that's the point of Immutable, instead of mutating the original collection you get a fresh new one.

This is how you do what you're trying to do with Immutable:

const { List } = require('immutable')

list = List([ List([]), List([]) ]);
list = list.set(0, list.get(0).push(2));
list = list.set(1, list.get(1).push(3));
list = list.set(0, list.get(0).push(4));
list = list.set(1, list.get(1).push(6));

console.log(list);

List [ List[2, 4], List[3, 6] ]