On every change detection cycle, Angular synchronously:
ngOnChangeslifecycle hooks. A single slow computation within a template or a lifecycle hook can slow down the entire change detection process because Angular runs the computations sequentially.
You can identify heavy computations with Angular DevTools’ profiler. In the performance timeline, click on a bar to preview a particular change detection cycle. This displays a bar chart, which shows how long the framework spent in change detection for each component. When you click on a component, you can preview how long Angular spent evaluating its template and lifecycle hooks.
For example, in the screenshot above, we selected the second change detection cycle after the profiler started where Angular spent over 573 ms. Angular spent most time in the
EmployeeListComponent. In the details panel, we can see that we spent over 297ms in evaluating the template of the
There are several techniques to eliminate slow computations:
Pure pipes and memoization have different trade-offs. Pure pipes are an Angular built-in concept compared to memoization, which is a general software engineering practice for caching function results. The memory overhead of memoization could be significant if you invoke the heavy computation frequently with different arguments.
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