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fix(core): stop debounce double-invoking a single leading+trailing call #198

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Merged
JosunLP merged 1 commit into from
Jul 6, 2026
Merged

fix(core): stop debounce double-invoking a single leading+trailing call #198

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6 changes: 5 additions & 1 deletion src/core/utils/function.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,11 @@ export function debounce<TArgs extends unknown[]>(
const now = Date.now();
if (leading && !leadingDone) {
leadingDone = true;
invoke(args, trailing, now);
// Clear pendingArgs on the leading invoke so a SINGLE call does not also
// fire the trailing edge. A subsequent call within the window re-sets
// pendingArgs (the leading branch is skipped), so the trailing edge still
// fires when the function was called more than once (lodash semantics).
invoke(args, false, now);
}
clearTrailing();
timeoutId = setTimeout(trailingTrigger, delayMs);
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6 changes: 4 additions & 2 deletions tests/utils-function-extras.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -121,15 +121,17 @@ describe('utils/function extras', () => {
expect(calls).toEqual([1, 3]);
});

it('debounce(leading: true, trailing: true) keeps a single call for the trailing edge', async () => {
it('debounce(leading: true, trailing: true) does not double-invoke a single call (#178)', async () => {
const calls: number[] = [];
const fn = debounce((n: number) => calls.push(n), 30, { leading: true, trailing: true });

fn(1);

// Leading fires immediately; the trailing edge must NOT fire for a single
// call (lodash semantics: trailing only when called more than once).
expect(calls).toEqual([1]);
await wait(60);
expect(calls).toEqual([1, 1]);
expect(calls).toEqual([1]);
});

it('debounce maxWait forces invocation', async () => {
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