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Don't pass undefined to custom equality checks on becoming observed a… #1213

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Nov 1, 2017
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Don't pass undefined to custom equality checks on becoming observed a… #1213

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Don't pass undefined to custom equality checks on becoming observed a…
Oct 19, 2017
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Oct 19, 2017
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2 changes: 1 addition & 1 deletion src/core/computedvalue.ts
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Expand Up @@ -110,7 +110,7 @@ export class ComputedValue<T> implements IObservable, IComputedValue<T>, IDeriva

onBecomeUnobserved() {
clearObserving(this)
this.value = undefined
this.value = new CaughtException(null)
}

/**
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2 changes: 1 addition & 1 deletion test/errorhandling.js
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Expand Up @@ -682,7 +682,7 @@ test("peeking inside autorun doesn't bork (global) state", t => {
t.equal(b.diffValue, 0)
t.equal(b.lowestObserverState, 0)
t.equal(b.unboundDepsCount, 1)
t.equal(b.value, undefined)
t.notEqual(b.value, 3)
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I'm not particularly happy with this assertion. I wanted to write something like t.ok(isCaughtException(b.value)) but as far as I can tell neither CaughtException nor isCaughtException are exported from mobx.ts. I considered exporting them from mobx.ts, but that's changing public API. Also considered importing them from core/derivation.ts directly, but that's inconsistent with all other tests.

This feels like it's still achieving the goal of the assertion (ensuring that the cached value is cleared) while avoiding those problems.

I'm open to suggestions of other approaches.

t.equal(b.isComputing, false)

t.equal(c.dependenciesState, -1)
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9 changes: 7 additions & 2 deletions test/observables.js
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Expand Up @@ -1853,7 +1853,7 @@ test("computed equals function only invoked when necessary", t => {
)

const values = []
const disposeAutorun = mobx.autorun(() => values.push(combinedToLowerCase.get()))
let disposeAutorun = mobx.autorun(() => values.push(combinedToLowerCase.get()))

// No comparison should be made on the first value
t.deepEqual(comparisons, [])
Expand All @@ -1879,7 +1879,12 @@ test("computed equals function only invoked when necessary", t => {
right.set("F")
t.deepEqual(comparisons, [{ from: "ab", to: "cb" }, { from: "de", to: "df" }])

t.deepEqual(values, ["ab", "cb", "de", "df"])
// Becoming unobserved, then observed won't cause a comparison
disposeAutorun()
disposeAutorun = mobx.autorun(() => values.push(combinedToLowerCase.get()));
t.deepEqual(comparisons, [{ from: "ab", to: "cb" }, { from: "de", to: "df" }])

t.deepEqual(values, ["ab", "cb", "de", "df", "df"])

disposeAutorun()

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