Helper not rerun when property changes - ember.js

Question

I'm trying to have a helper output nutrient totals based on a list (array) of ingredients. Since I want to display the totals of one of many nutrients I need to somehow pass it a parameter that defines the nutrient in question. So I figured a helper would be the way to go, something like this:
{{nutrient-total list "kcal"}}
The problem is that the helper is only rendered/run once. However, the {{#each}} helper is updated when a new item is pushed to the list so it seems to be possible. I think I am missing something here. Should helpers be run again if a parameter changes, or should I be trying something else?
The list looks like this:
{
ingredient: {
name: 'Potato',
group: 'Veggies',
nutrients: [{
name: 'kcal',
nutritionalValue: 87
}, {
name: 'kJ',
nutritionalValue: 42
}]
},
weight: 42
}
For future reference:
The solution with a helper:
Twiddle
The solution with a computed property
Twiddle

Answer 1

Your list objects is plain objects but you deal with like ember object.
I mean you shouldn't use get for those.
list.forEach(item => {
let weight = item.weight;
item.ingredient.nutrients.forEach(nutrient => {
if (nutrient.name === unit) {
total += weight * nutrient.nutritionalValue;
}
});
});
But if you want to work for all types, use Ember.get like this :
const {get} = Ember;
...
list.forEach(item => {
let weight = get(item, 'weight');
get(get(item, 'ingredient'), 'nutrients').forEach(nutrient => {
if (get(nutrient, 'name') === unit) {
total += weight * get(nutrient, 'nutritionalValue');
}
});
});
UPDATE
The main reason that helper doesn't work is that the list property should be notified.
In action you need to call this.notifyPropertyChange('list'); at the end.
Also to get rid of this you can create a class based helper

Answer 2

Instead of helper you can very well use computed property,
total: Ember.computed('list.[]','unit', function() {
let total = 0;
list.forEach(item => {
let weight = item.get('weight');
item.ingredient.get('nutrients').forEach(nutrient => {
if (nutrient.name === unit) {
total += weight * nutrient.nutritionalValue;
}
});
});
return total;
})
Reason for not running the helper might be, we are not changing the reference of list