Passing equals option to computedFn does not change behaviour

I’m trying to pass an options object to computedFn() with the equals property to set the comparer function to use.

filterForIndividual = computedFn(function(individualsId) {
    return this.filter((id, item) => ThObj.value(item, ThIdSessions.INDIVIDUALS_ID) === individualsId);
}, { equals: comparer.structural, });

The problem is that it always uses the comparer.default comparer. I have set a debug point in mobx.comparer.ts file and it never enters in the structuralComparer() method and always use defaultComparer().

I have tried to simplify the real code in a CodeSandbox and try to understand what is happening. The problem can be reproduced, no matter what the comparer value you set, the computedFn() always runs - so it is not caching - even if the returned data is the same (not same reference).

https://codesandbox.io/s/pedantic-yonath-owtvt?file=/src/App.js

Inspecting the source code seems that computedFn() can accept an options object and pass it throught to computed(), so there must be something I am missing .

[DavidCasillasRivero]

Of course, you are right, I had this sentence from MobX and completely misunderstood it.

“Computed values can be used to derive information from other observables. They evaluate lazily, caching their output and only recomputing if one of the underlying observables has changed. If they are not observed by anything, they suspend entirely.”

I updated the codesandbox and the re-render only happens using comparer.identity as expected.

So the problem in my original code must be somewhere else, and the options passed to computedFn are working. Thanks for the super fast response.

[urugator]

Try:

const t = new Test();

autorun(() => {
  console.log("autorun");  
  const map = t.filterStructural()  
})

t.increment();
t.increment();
t.increment();

There is just a single “autorun” in console as opposed to using t.filterIdentity (4).