Debugging Performance Problems
By the end of this lesson, you'll be able to:
- Use the browser DevTools Performance panel to profile a slow component
- Recognize the common culprits behind LWC performance problems
- Work through a realistic performance diagnosis systematically
Prerequisites: "Component Composition for Performance"
Using the Performance Panel
Browser DevTools' Performance panel can record a profile while interacting with a slow component — clicking "Record," performing the slow interaction, then stopping. The resulting timeline highlights long-running tasks and where script execution time is actually being spent, turning a vague "it feels slow" into concrete, measured data. Module 14 covers DevTools more broadly for general debugging; this lesson focuses specifically on using it for performance profiling.
Common Culprits
This module's own lessons double as a diagnostic checklist:
- Redundant server calls (Lesson 1) — inconsistent wire parameters defeating caching, or components each making calls that could share a cache entry.
- Expensive, unmemoized getters (Lesson 2) — heavy computation re-running on every render rather than only when its input changes.
- Unpaginated large lists (Lesson 3) — too many DOM nodes rendered at once.
- Poor component composition (Lesson 4) — either one giant component re-rendering everything on any small change, or excessive over-splitting adding boundary overhead.
A Worked Diagnostic Walkthrough
A component listing Accounts feels sluggish whenever the user types in a search box. Working through the checklist:
- Is a server call happening on every keystroke, with parameters that vary just enough (unnormalized casing/whitespace) to defeat wire caching? → Lesson 1's fix.
- Is the filtered/sorted list computed inside a getter that's doing more work than necessary on every keystroke's re-render? → Lesson 2's fix.
- Is the full unfiltered dataset — potentially thousands of rows — being rendered rather than a paginated subset? → Lesson 3's fix.
Working through these in order, rather than guessing, is what turns "it's slow" into a specific, addressable cause.
Exercise
A datatable becomes sluggish specifically while typing into a search box. Walk through, as a comment, the first two things from this module's checklist worth checking.
Show hint
Think about what happens on every single keystroke.
Exercise
Challenge: explain, as a comment, why recording a Performance panel profile is preferable to guessing at the cause of a slow component.
Show hint
Think about the difference between a hunch and measured data.
Debugging Performance Problems Quiz
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Summary
A structured approach — profile first, then check against the common culprits from this module — turns "the component feels slow" into a specific, fixable root cause.