Designing a public API for a JavaScript module

Question

I am writing a module that can access localStorage through a public API which exposes methods that allow string or array returns.

It doesn't feel as though I'm doing this in the most effective way. For example, I feel as though using:

var tudCache = getTud(); to grab the object from getTud() doesn't feel like the most correct implementation.

I'm inclined to use an if statement i.e. if(getTud().isSuccessful) to check the conditional but then I would have to re-execute getTud().result to return the result inside that conditional, causing the getTud() function to be called twice.

Does anyone have any thoughts?

_self.getTudCache = function () {

    // returns an object. {'isSuccessful': boolean, 'result': String}
    function getTud() {

        return localstorage.getItem(tudStorageKey);

    }

    function getString() {

        var tudCache = getTud();

        if (tudCache.isSuccessful)
            return tudCache.result;
        return "";

    }

    function getArr() {

        var tudCache = getTud();

        if (tudCache.isSuccessful)
            return JSON.parse(tudCache.result)[tudCacheKey];
        return [];
    }

     return {
         getString: getString,
         getArr: getArr
     }
};

Answer 1

It seems to me that it'd be simpler to always use JSON, rather than limit yourself to strings and arrays, specifically.

E.g.

function retrieve(key) {
  var json = localStorage.getItem(key);
  try {
    return JSON.parse(json).value;
  } catch(e) {
    return json; // either null or a non-comforming value
  }
}

function store(key, value) {
  var json = JSON.stringify({ value: value });
  localStorage.setItem(key, json);
}

This will let you store and retrieve any JSON-serializable value including strings and arrays. You can wrap/namespace it however you like.