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Avoid constructor source scanning for classes without a base class in @loopback/context

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
node.js, typescript
Domain
backend, performance

Research direction

Start by reading describeInjectedArguments() and shouldSkipBaseConstructorInjection() in @loopback/context, then check the existing tests for constructor injection and inheritance. Confirm that classes without a base class avoid the source scan while classes with a base class retain the existing behavior; run the relevant tests to verify both cases.

Written by the indexing model from the issue text.

Description

bug
Describe the bug

On the first call to describeInjectedArguments() for a constructor, LoopBack calls shouldSkipBaseConstructorInjection(), which reads the class’s source and runs regular expressions to determine whether constructor injections should be inherited.

This work also runs for classes that do not extend another class. For those classes, there is no base constructor to inspect. The metadata cache avoids repeated work for the same class, but applications inspecting many distinct classes still incur this cost during startup.

The proposed change in describeInjectedArguments() is:

if (method === '') {
  if (
    Object.getPrototypeOf(target) !== Function.prototype &&
    shouldSkipBaseConstructorInjection(target)
  ) {
    options.ownMetadataOnly = true;
  }
}
Logs
Additional information

We measured the following application startup timings with @loopback/context 9.0.0, Node.js 22.23.4, and macOS 26.7 on an Apple M4 Pro:

Measurement Original With proposed guard
Constructor inspection 147.9 ms 18.5 ms
Overall component registration 224 ms 98 ms

These are medians of three fresh processes per variant, alternating between variants with other startup settings held constant. Of 3,948 inspected classes, 3,384 had no base class.

The improvement saves approximately 126 ms during registration. Constructor inspection is included in registration, so these savings are not additive or a claim about total application startup time.

Reproduction

https://github.com/tonynelson19/loopback-constructor-repro

Dominant language
TypeScript
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