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fix(useThrottleFn)!: align with traditional throttle behavior #4923

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@IceMooncake IceMooncake commented Jul 30, 2025 •
edited by ilyaliao
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Description

This PR fixes an inconsistency in useThrottleFn's behavior when leading: false, making it behave more like lodash.throttle.

Previously, when leading was set to false, the function could still execute on the second call if the first call was suppressed. This was because lastExec was not updated when the call was skipped, resulting in incorrect elapsed calculation.

This PR updates the logic to ensure that the throttle interval is respected properly, even when leading: false. This change aligns the behavior with developers’ expectations and lodash's semantics.

Fixes #4920.
Fixes #4551.

Additional context

  • The issue arises because VueUse treats the “last execution time” as the moment when the function actually runs, rather than when it is called.
  • In contrast, Lodash updates the timestamp immediately when the throttled function is invoked (even if suppressed).
  • This led to confusion when leading: false, as the second call would unexpectedly pass through the throttle.
  • Test cases have been adjusted to validate the new behavior.

Original issue discussion: [#4920](#4920)

@dosubot dosubot bot added the size:S This PR changes 10-29 lines, ignoring generated files. label Jul 30, 2025
@dosubot dosubot bot added size:M This PR changes 30-99 lines, ignoring generated files. and removed size:S This PR changes 10-29 lines, ignoring generated files. labels Jul 30, 2025
@OrbisK OrbisK requested a review from ilyaliao July 30, 2025 09:17
@OrbisK OrbisK changed the title fix(useThrottleFn): align with traditional throttle behavior (#4920) fix(useThrottleFn): align with traditional throttle behavior Jul 31, 2025
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commit: 4bd9256

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Hi @ilyaliao , thank you for maintaining VueUse 🙏
This PR fixes useThrottleFn(#4920) and has passed all CI checks.
When you have time, could you please review it? Thanks a lot!

ilyaliao
ilyaliao previously approved these changes Aug 14, 2025
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LGTM :>

@dosubot dosubot bot added the lgtm This PR has been approved by a maintainer label Aug 14, 2025
OrbisK
OrbisK previously approved these changes Aug 14, 2025
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Here's a demo demonstrating the behavioral differences between VueUse throttle and Lodash.

https://playground.vueuse.org/?vueuse=13.6.0#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

@ilyaliao ilyaliao changed the title fix(useThrottleFn): align with traditional throttle behavior fix(useThrottleFn)!: align with traditional throttle behavior Aug 14, 2025
@IceMooncake IceMooncake dismissed stale reviews from OrbisK and ilyaliao via 4bd9256 August 15, 2025 01:26
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IceMooncake commented Aug 15, 2025 •
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@ilyaliao Sorry, I missed this in my earlier review. Just noticed a pair of redundant parentheses — submitted a new commit that only removes the parentheses around leading || !isLeading.

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BUG | useThrottleFn | leading false option doesn't work properly BUG | refThrottled | The option leading: false seems to be ignored
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