Microsoft/TypeScript

Code generated for optional call could be optimized when the result is unused

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#38,835 opened on May 28, 2020

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Effort: ModerateExperience EnhancementHelp WantedSuggestion

Description

The generated code for optional chaining is a little verbose when the "return" value of the expression is not being used. For example, when simply calling a function:

maybe.close?.()

Here is a more complete example.

The second example generates:

(_c = (_b = perhaps.maybe) === null || _b === void 0 ? void 0 : _b.close) === null || _c === void 0 ? void 0 : _c.call(_b);

But could be optimized to:

(_b = perhaps.maybe) !== null && _b !== void 0 && (_c = _b.close) !== null && _c !== void 0 && _c.call(_b);

It's not a huge difference, but it saves 8 characters for each link in the chain.

While the spec says something like: "the expression short-circuits with a return value of undefined", when the return value is meaningless, then only the "short-circuit" part is important.

Contributor guide

Tech stack
typescript
Domain
performance
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
TypeScript compiler internalsOptional chaining semantics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Investigate the TypeScript compiler's emitter (src/compiler/emitter.ts) where optional chaining code is generated. The current output checks for null/void separately for each chain link. The proposed optimization uses a shorter form when the result is unused. Examine existing tests for optional chaining to ensure no semantic change. The issue is open with no recent discussion; a good starting point is to comment on the issue and seek maintainer input on whether such an optimization is desired and if there are any edge cases to consider.