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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →When an Angular interaction feels slow, profile a representative interaction before changing code. A costly template expression or lifecycle hook can hold up a change-detection cycle because Angular evaluates applicable work synchronously and sequentially. Use Angular DevTools to find what is taking time, then choose a fix for that measured bottleneck.
Why a slow computation affects Angular interactions
During change detection, Angular evaluates applicable template expressions and selected lifecycle hooks synchronously. Since that work runs sequentially, one expensive computation can delay the rest of the cycle. The issue may be a costly algorithm, repeated work, or unnecessary DOM operations—not necessarily change detection as a whole. Angular’s slow-computations guidance explains this behavior.
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This is a runtime-performance problem: it concerns work associated with change detection. It is distinct from slow initial loading, which Angular treats separately with techniques such as deferred loading, image optimization, and server-side rendering. Angular’s performance overview covers those broader categories.
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How to locate the bottleneck
- Record a representative interaction. Open Angular DevTools, select the Profiler, and record the interaction that exhibits the delay.
- Select a slow change-detection cycle. Inspect its component/directive chart or flame graph to see where time is spent.
- Inspect the component details. Look for an expensive template evaluation, lifecycle hook, or other work that dominates the cycle, and focus on that specific computation.
- Use the measurements to choose a fix. The profiler reports cycle time and can estimate frame rate when it falls below 60 fps. Angular’s DevTools Profiler guide describes the profiler views and their use.
Angular’s documentation illustrates a single cycle taking over 573 ms, with over 297 ms spent evaluating the EmployeeListComponent template. Those figures describe that documentation example only; they are not a benchmark or an expected result for Angular applications. See Angular’s example and guidance.
#1 Best Overall
Which optimization fits the measured work?
There is no universal best fix. Start with the computation that profiling identified, and consider how often its inputs change and what retaining cached results would cost.
| Approach | When it fits | Trade-off or behavior |
|---|---|---|
| Improve the algorithm | The computation itself does more work than necessary. | Angular recommends optimizing the underlying algorithm first. |
| Pure pipe | A template transformation can benefit from Angular-managed caching. | Recomputes when Angular detects changed inputs. |
| Memoization | Repeated calls with the same arguments can reuse stored results. | Can retain multiple argument/result pairs; memory use may become significant when many different arguments are used frequently. |
| Computed signal | Expensive derived state depends on signals. | Evaluation is lazy and memoized; a tracked dependency change invalidates the cached result. |
| Change-detection scope or frequency | Profiling indicates broad or excessive change detection rather than one dominant expression. | Use runtime-performance guidance to assess options such as OnPush subtree skipping, zoneless change detection, or zone pollution. |
Angular’s recommendations for algorithm improvements, pure pipes, and memoization are in its slow-computations guide. For signal-based derived state, see Angular’s signals guide.
Use computed signals for derived signal state
A computed() signal is lazy and memoized: Angular evaluates its derivation when the value is read, caches the result, and invalidates that result when a tracked dependency changes. This can suit expensive derived work, such as filtering an array, when the relevant inputs are signals. The computation should read the signals that represent its dependencies so Angular can track invalidation correctly.
Keep effects for synchronizing signal state with imperative, non-signal APIs. Angular recommends computed() or linkedSignal() for derived values; using effects to propagate state changes can trigger unnecessary change-detection cycles. See Angular’s effect guidance.
Rank #3
Keep DOM layout work out of recurring hooks
Repeated DOM access, repainting, and reflow can add substantial work. DOM mutations can trigger reflows, so avoid putting unnecessary layout reads or writes in lifecycle hooks that run repeatedly.
When custom DOM work is necessary, Angular’s afterRenderEffect provides phases intended to group operations and help avoid layout thrashing. Use it for appropriate DOM work rather than as a substitute for measuring the actual bottleneck. See Angular’s render-effect guidance.
When the problem is broader than one expression
If the profiler does not show a single expensive template expression or hook, inspect whether change detection is happening too broadly or too often. Angular’s runtime-performance guidance discusses zoneless change detection, skipping subtrees with OnPush, and zone pollution. Zoneless change detection is the default for new applications in Angular v21 and later; check the target application’s version and migration context before applying version-specific advice. Start with Angular’s performance overview and the Profiler guide.
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