React useCache Hook Implementation

This challenge asks you to build a custom React hook, useCache, that intelligently caches the results of asynchronous operations. This is a common pattern for optimizing performance in React applications by preventing redundant API calls or expensive computations, leading to a smoother user experience.

Problem Description

You need to implement a useCache hook in TypeScript that takes a function as an argument and returns a new function. This new function, when called, should execute the original function. However, if the original function has already been called with the exact same arguments, the hook should return the cached result instead of re-executing the original function.

Key Requirements:

• Caching Mechanism: Store the results of function calls, keyed by their arguments.
• Argument Matching: The hook must accurately compare arguments to determine if a cache hit has occurred. Primitive types (strings, numbers, booleans, null, undefined, symbols, bigints) should be compared by value. For object types (arrays, objects), a deep comparison is required to ensure that structurally identical arguments are considered the same.
• Asynchronous Function Support: The hook should gracefully handle functions that return Promises. The cache should store the resolved value of the Promise.
• Return Value: The hook should return a memoized function that mirrors the signature of the input function.
• Type Safety: The implementation must be robust and type-safe using TypeScript.

Expected Behavior:

1. When the returned function is called for the first time with a specific set of arguments, the original function is executed.
2. The result of the original function is stored in the cache, associated with the arguments used.
3. Subsequent calls to the returned function with the exact same arguments will retrieve and return the cached result without re-executing the original function.
4. If the original function is asynchronous (returns a Promise), the hook should wait for the Promise to resolve and then cache and return its resolved value.

Edge Cases to Consider:

• Functions with no arguments.
• Functions with varying numbers and types of arguments, including null and undefined.
• Object and array arguments that are structurally the same but not referentially identical.
• Handling of stale cache entries (though for this challenge, we'll assume a simple in-memory cache that doesn't expire).

Examples

Example 1: Basic Function Caching

import React, { useState, useEffect } from 'react';
import { useCache } from './useCache'; // Assume useCache is in this file

const simulateFetch = (id: number): Promise<string> => {
  console.log(`Fetching data for id: ${id}...`);
  return new Promise(resolve => {
    setTimeout(() => resolve(`Data for ${id}`), 1000);
  });
};

function App() {
  const [data1, setData1] = useState<string | null>(null);
  const [data2, setData2] = useState<string | null>(null);

  const cachedFetch = useCache(simulateFetch);

  useEffect(() => {
    const fetchData = async () => {
      const result1 = await cachedFetch(1);
      setData1(result1);

      // This call should hit the cache
      const result2 = await cachedFetch(1);
      setData2(result2);
    };
    fetchData();
  }, [cachedFetch]);

  return (
    <div>
      <h1>useCache Example 1</h1>
      <p>Data 1: {data1}</p>
      <p>Data 2: {data2}</p>
    </div>
  );
}

export default App;

Expected Console Output:

Fetching data for id: 1...

Explanation:

The simulateFetch function is called only once for id = 1. The second call to cachedFetch(1) retrieves the result directly from the cache, preventing a second network request.

Example 2: Caching with Different Arguments

import React, { useState, useEffect } from 'react';
import { useCache } from './useCache';

const simulateAdd = (a: number, b: number): number => {
  console.log(`Adding ${a} and ${b}...`);
  return a + b;
};

function App() {
  const [sum1, setSum1] = useState<number | null>(null);
  const [sum2, setSum2] = useState<number | null>(null);
  const [sum3, setSum3] = useState<number | null>(null);

  const cachedAdd = useCache(simulateAdd);

  useEffect(() => {
    const calculateSums = () => {
      const result1 = cachedAdd(5, 3);
      setSum1(result1);

      const result2 = cachedAdd(5, 3); // Cache hit
      setSum2(result2);

      const result3 = cachedAdd(10, 2); // New arguments, cache miss
      setSum3(result3);
    };
    calculateSums();
  }, [cachedAdd]);

  return (
    <div>
      <h1>useCache Example 2</h1>
      <p>Sum 1 (5 + 3): {sum1}</p>
      <p>Sum 2 (5 + 3): {sum2}</p>
      <p>Sum 3 (10 + 2): {sum3}</p>
    </div>
  );
}

export default App;

Expected Console Output:

Adding 5 and 3...
Adding 10 and 2...

Explanation:

The simulateAdd function is called for (5, 3) and then for (10, 2). The second call with (5, 3) is a cache hit.

Example 3: Caching with Object Arguments (Deep Comparison)

import React, { useState, useEffect } from 'react';
import { useCache } from './useCache';

interface User {
  id: number;
  name: string;
}

const simulateGetUserProfile = (user: User): Promise<string> => {
  console.log(`Fetching profile for user: ${user.name} (ID: ${user.id})...`);
  return new Promise(resolve => {
    setTimeout(() => resolve(`Profile for ${user.name}`), 800);
  });
};

function App() {
  const [profile1, setProfile1] = useState<string | null>(null);
  const [profile2, setProfile2] = useState<string | null>(null);

  const cachedGetUserProfile = useCache(simulateGetUserProfile);

  useEffect(() => {
    const fetchProfiles = async () => {
      const user1 = { id: 101, name: 'Alice' };
      const user2 = { id: 101, name: 'Alice' }; // Structurally identical to user1

      const result1 = await cachedGetUserProfile(user1);
      setProfile1(result1);

      // This call should hit the cache because user2 has the same structure as user1
      const result2 = await cachedGetUserProfile(user2);
      setProfile2(result2);
    };
    fetchProfiles();
  }, [cachedGetUserProfile]);

  return (
    <div>
      <h1>useCache Example 3</h1>
      <p>Profile 1: {profile1}</p>
      <p>Profile 2: {profile2}</p>
    </div>
  );
}

export default App;

Expected Console Output:

Fetching profile for user: Alice (ID: 101)...

Explanation:

Even though user1 and user2 are different object instances, they represent the same data. The useCache hook should perform a deep comparison of the arguments and recognize that cachedGetUserProfile(user2) should be a cache hit after cachedGetUserProfile(user1).

Constraints

• The hook must be implemented in TypeScript.
• The cache should be an in-memory cache within the hook's scope. No external storage or persistence is required.
• Argument comparison for objects and arrays must be a deep equality check. You may use a utility function for deep comparison if available or implement a basic one.
• The original function can be synchronous or asynchronous (returning a Promise).
• The hook should handle up to 5 arguments for the cached function. (This constraint can be relaxed by using rest parameters ...args and a more sophisticated key generation, but for this challenge, focusing on a fixed number simplifies argument handling and comparison).
• Performance: For typical usage with a reasonable number of cached calls, the lookup and retrieval should be very fast.

Notes

• Consider how to generate a unique cache key for each unique set of arguments. For primitive types, this is straightforward. For objects and arrays, a stringified or serialized representation might be useful, but ensure it handles the deep equality requirement.
• You will need to manage the cache state within the hook. useRef might be a good candidate for storing the cache data without causing re-renders.
• Think about the return type of the hook. It should be a function that mirrors the input function's signature but with the cached behavior.
• For deep comparison of objects and arrays, you can leverage libraries like Lodash's isEqual if allowed, or implement a simplified recursive deep equality check yourself. For this challenge, a basic recursive implementation for plain objects and arrays should suffice.