withCallCount

Wraps a function and tracks how many times the wrapper is invoked.

Code

withCallCount.ts

export type CallCountControls = {
  readonly getCallCount: () => number;
  readonly resetCallCount: () => void;
};

export type CountedFunction<
  Arguments extends unknown[],
  Return,
  This = unknown,
> = ((
  this: This,
  ...args: Arguments
) => Return) & CallCountControls;

type AnyFunction = (this: never, ...args: never[]) => unknown;
type CallCountGuard<Function extends AnyFunction> =
  Extract<keyof Function, keyof CallCountControls> extends never ? [] : never;

/** Wraps a function and tracks how many times the wrapper is invoked. */
export const withCallCount = <Function extends AnyFunction>(
  fn: Function,
  ..._guard: CallCountGuard<Function>
): Function & CallCountControls => {
  if ("getCallCount" in fn || "resetCallCount" in fn) {
    throw new TypeError(
      'fn must not define "getCallCount" or "resetCallCount" properties'
    );
  }

  let callCount = 0;

  const getCallCount = () => callCount;
  const resetCallCount = () => {
    callCount = 0;
  };

  return new Proxy(fn, {
    apply(target, receiver, args) {
      callCount += 1;
      return Reflect.apply(target, receiver, args);
    },
    get(target, property, receiver) {
      if (property === "getCallCount") return getCallCount;
      if (property === "resetCallCount") return resetCallCount;
      return Reflect.get(target, property, receiver);
    },
    has(target, property) {
      return (
        property === "getCallCount" ||
        property === "resetCallCount" ||
        Reflect.has(target, property)
      );
    },
    set(target, property, value, receiver) {
      return property === "getCallCount" || property === "resetCallCount"
        ? false
        : Reflect.set(target, property, value, receiver);
    },
  }) as Function & CallCountControls;
};

Download

wget

Terminal

wget -O src/lib/withCallCount.ts https://raw.githubusercontent.com/jrTilak/lazykit/HEAD/registry/functions/withCallCount.ts

degit

Terminal

temp_dir="$(mktemp -d)" && bunx degit jrTilak/lazykit/registry/functions "$temp_dir" && mv "$temp_dir/withCallCount.ts" src/lib/withCallCount.ts && rm -r "$temp_dir"

Examples

withCallCount.example.ts

import { withCallCount } from "./withCallCount";

const add = withCallCount((left: number, right: number) => left + right);

console.log(add(3, 5)); // 8
console.log(add(2, 7)); // 9
console.log(add.getCallCount()); // 2

add.resetCallCount();
console.log(add.getCallCount()); // 0

Props

• fn ((...args: A) => R) — Function whose wrapper invocations should be counted; its receiver is preserved.

Returns

The wrapped function with getCallCount() and resetCallCount() methods. Calls are counted even when fn throws. Properties on a callable object remain available through the wrapper. Callables that already define either control name are rejected.