检查chrome.storage.sync中是否已经存在数据

Question

I have a function that gets data from chrome.storage and loads it into an array, everything works fine if I save an empty array into chrome.storage using a line of code then taking it out before using the extension as a user would.

The problem is that a user couldn't do that, if I start the extension for the first time without doing this then it looks like chrome passes back undefined into the variable which causes this error:

"Uncaught TypeError: Cannot read property '8' of undefined"

at this line:

if (SavedReminders[i][8] == "Full") {

I'm not entirely sure what exactly is going on, but I guess that if there's a way to check if the data exists already in chrome.storage or a way of saving an empty array just the first time the user opens the extension that would fix it.

Here's my Load function:

function LoadFromFile() {
    reminds = {}
    chrome.storage.sync.get({ reminds: [] }, function (result) { SavedReminders = result.reminds });
}

and save function:

function SaveToFile() {
    reminds={}
    chrome.storage.sync.set({reminds:SavedReminders }, 
        function () {
            console.log(SavedReminders, reminds);
        });
}

any help would be appreciated, thanks.

Answer 1

You can pass an object to the api (instead of an array of keys) with default values for each key. It will return the default value for keys that arent there.
you can also just leave it as is and check if its ==undefined but my suggested way is cleaner.
details about how to pass such object are on the official api docs for .storage:

https://developer.chrome.com/extensions/storage StorageArea methods:get StorageArea.get(string or array of string or object keys, function callback) (optional) keys: ..."or a dictionary specifying default values"...

so chrome.storage.local.get({foo:"hi", bar:"there"}) will return obj where obj["foo"] is "hi" when not yet saved.

Answer 2

In my case, I was looking for a dictionary and the call seemed to be returning some kind of prototype object along with the dictionary (so the object type wasn't "undefined"). To get the value I was actually looking for, I had to check the property of the returned object.

chrome.storage.sync.get('profile', function(profileObj) {
  var profile = profileObj.profile;
  if (typeof profile === "undefined") {
    // No profile in storage
  } else {
    // Profile exists in storage
  }
});

Answer 3

Also you can check if storage.sync or storage.local returns an uninitialized storage using empty object detection:

function _empty(o) {
    return Object.keys(o).length === 0 && o.constructor === Object
}

So the line if (SavedReminders[i][8] == "Full") { will become either if(!_empty(SavedReminders)) or if (SavedReminders && SavedReminders[i] && SavedReminders[i][8] == "Full") { .