CachingDecorator.md

function slow(x) {

  // there can be a heavy CPU-intensive job here

  alert(`Called with ${x}`);

  return x;

}

 

function cachingDecorator(func) {

  let cache = new Map();

 

  return function(x) {

    if (cache.has(x)) { // if the result is in the map

      return cache.get(x); // return it

    }

 

    let result = func(x); // otherwise call func

 

    cache.set(x, result); // and cache (remember) the result

    console.log(cache);

    return result;

  };

}

 

slow = cachingDecorator(slow);

 

console.log( slow(1) ); // slow(1) is cached

console.log( "Again: " + slow(1) ); // the same

 

console.log( slow(2) ); // slow(2) is cached

console.log( "Again: " + slow(2) ); // the same as the previous line