How do I get a specific object from an immutable js map by value?

Question

I created an immutable map (with Immutable-JS) from a list of objects:

var result = [{'id': 2}, {'id': 4}]; var map = Immutable.fromJS(result); 

Now i want to get the object with id = 4.

Is there an easier way than this:

var object = map.filter(function(obj){  return obj.get('id') === 4 }).first(); 

Answer 1

Essentially, no: you're performing a list lookup by value, not by index, so it will always be a linear traversal.

An improvement would be to use find instead of filter:

var result = map.find(function(obj){return obj.get('id') === 4;}); 

Answer 2

The first thing to note is that you're not actually creating a map, you're creating a list:

var result = [{'id': 2}, {'id': 4}]; var map = Immutable.fromJS(result);  Immutable.Map.isMap(map); // false Immutable.List.isList(map); // true 

In order to create a map you can use a reviver argument in your toJS call (docs), but it's certainly not the most intuitive api, alternatively you can do something like:

// lets use letters rather than numbers as numbers get coerced to strings anyway var result = [{'id': 'a'}, {'id': 'b'}]; var map = Immutable.Map(result.reduce(function(previous, current) {      previous[ current.id ] = current;     return previous; }, {}));  Immutable.Map.isMap(map); // true 

Now we have a proper Immutable.js map which has a get method

var item = Map.get('a'); // {id: 'a'}