How is this JavaScript function caching its results?

Question

After reading over it several times, I still don't understand how this example code from page 76 of Stoyan Stefanov's "JavaScript Patterns" works. I'm not a ninja yet. But to me, it reads like it's only storing an empty object:

var myFunc = function (param) {
  if (!myFunc.cache[param]) {
    var result = {};
    // ... expensive operation ...
    myFunc.cache[param] = result;
  } 
  return myFunc.cache[param];
};
// cache storage
myFunc.cache = {};

Unless that unseen "expensive operation" is storing back to result, I don't see anything being retained.

Where are the results being stored?

P.S.: I've read Caching the return results of a function from John Resig's Learning Advanced JavaScript, which is a similar exercise, and I get that one. But the code is different here.

Answer 1

You've answered your own question -- the author assumes that the expensive operation will store its result in result.

The cache would otherwise only contain empty objects, as you've noted.