Cache middleware pattern in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a cache object in Express middleware.

Express

const cache = [1]();

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Anew Array

Bnew Set

Cnew Object

Dnew Map

Attempts:

3 left

💡 Hint

Common Mistakes

Using new Set instead of Map, which only stores unique values without keys.

Using new Array which is not suitable for key-value caching.

We use new Map() to create a cache object that stores key-value pairs efficiently.

2fill in blank

medium

Complete the middleware function to check if the cache has the requested URL.

Express

function cacheMiddleware(req, res, next) {
  if (cache.[1](req.url)) {
    res.send(cache.get(req.url));
  } else {
    next();
  }
}

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Ahas

Bincludes

Ccontains

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using includes or contains which are not methods of Map.

Using exists which is not a JavaScript method.

The Map object uses the has method to check if a key exists.

3fill in blank

hard

Fix the error in the middleware to store the response body in cache after sending it.

Express

function cacheMiddleware(req, res, next) {
  if (cache.has(req.url)) {
    res.send(cache.get(req.url));
  } else {
    const originalSend = res.send;
    res.send = function(body) {
      cache.set(req.url, [1]);
      originalSend.call(this, body);
    };
    next();
  }
}

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Ares.body

Bthis.body

Cbody

Dreq.body

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access res.body which is undefined.

Using req.body which is the request data, not response.

The body parameter contains the response content to cache.

4fill in blank

hard

Fill both blanks to create a cache middleware that stores JSON responses.

Express

function cacheMiddleware(req, res, next) {
  if (cache.has(req.url)) {
    res.json(cache.get(req.url));
  } else {
    const originalJson = res.json;
    res.json = function([1]) {
      cache.set(req.url, [2]);
      originalJson.call(this, [1]);
    };
    next();
  }
}

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Adata

Bres.body

Dbody

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names for the parameter and cache value.

Trying to use res.body which is not defined.

The parameter data holds the JSON response body, which we store in cache before sending.

5fill in blank

hard

Fill all three blanks to implement cache middleware with expiration time.

Express

const cache = new Map();
const cacheExpiry = new Map();
const CACHE_DURATION = 60000; // 1 minute

function cacheMiddleware(req, res, next) {
  const now = Date.now();
  if (cache.has(req.url) && cacheExpiry.get(req.url) > [1]) {
    res.send(cache.get(req.url));
  } else {
    const originalSend = res.send;
    res.send = function([2]) {
      cache.set(req.url, [3]);
      cacheExpiry.set(req.url, Date.now() + CACHE_DURATION);
      originalSend.call(this, [2]);
    };
    next();
  }
}

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Anow

Bbody

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined variables for time comparison.

Mixing up parameter names for the response body.

We compare the current time now to the stored expiry time. The body parameter is cached and sent.