Why might an Angular signal update fail to refresh the UI?

Diagnoses in-place mutation, equality rules, missing reactive reads, and incorrect use of untracked state.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

I first check whether the code called set or update with a new value instead of mutating an object or array in place. Signals use referential equality by default, so reusing the same reference can suppress the change. I then verify that the template or computed value read the signal in a tracked context and that a custom equality function or untracked call did not intentionally hide the dependency.

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Practice focus

Signal equality, immutable updates, dependency tracking, `untracked`, debugging, and rendering.

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Answer path

Core answer first, then checkpoints toward a stronger answer.

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Core answer
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Overview
A signal notifies consumers when its value is considered different and the consumer actually tracked the read.
I first check whether the code called set or update with a new value instead of mutating an object or array in place. Signals use referential equality by default, so reusing the same reference can suppress the change. I then verify that the template or computed value read the signal in a tracked context and that a custom equality function or untracked call did not intentionally hide the dependency.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
For a list, I would replace it with a new array containing the edited item rather than push into the existing array and set the same reference. I inspect conditional computed branches because Angular tracks only dependencies read during the latest calculation. A deep equality function may also discard an update that the UI considers meaningful, while an overly permissive immutable pattern can allocate without changing semantics. The fix should restore a clear state transition, not force change detection globally.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Mutating a signal's array or object and reusing the same reference.
Adding manual change detection before checking the state transition.
Using untracked to suppress a dependency that affects the output.

Why might an Angular signal update fail to refresh the UI?

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