es-toolkit/docs/reference/function/after.md

after

Creates a function that only executes starting from the n-th call. The provided function will be invoked starting from the n-th call.

The is particularly useful for scenarios involving events or asynchronous operations where an action should occur only after a certain number of invocations.

Signature

function after<F extends (...args: any[]) => any>(
  n: number,
  func: F
): (...args: Parameters<F>) => ReturnType<F> | undefined;

Parameters

• n (number): The number of calls required for func to execute.
• func (F): The function to be invoked.

Returns

((...args: Parameters<F>) => ReturnType<F> | undefined): A new function that:

• Tracks the number of calls.
• Invokes func starting from the n-th call.
• Returns undefined if fewer than n calls have been made.

Throws

Throws an error if n is negative.

Examples

import { after } from 'es-toolkit/function';

const mockFn = () => {
  console.log('called');
};
const afterFn = after(3, mockFn);

// Will not log anything.
afterFn();
// Will not log anything.
afterFn();
// Will log 'called'.
afterFn();