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
 }
};

• Joseph: I'm not even sure this code works. localStorage.getItem return strings, not objects. Can you add in the rest of the code, as well as a simple demo?
• nikk wong: I should have clarified that we're using a wrapper for localStorage. See this plnkr: plnkr.co/edit/y7eS0R22g0dRkbG4U3US?p=catalogue Thanks!

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.