Mozilla localStorage.getItem based on partial knowlege of an unique key

user_1816260 0
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I am looking for quick way to get an item from the Mozilla localStorage based on partial knowledge of an unique key. I have the following structure defined as the key : value

UUID1 : "BLABLABLA": UUID2 : Value

Where the key part looks like this for example:

ca4417f4-f83b-11eb-bf45-ffc420139ccb:BLABLABLA:e1d26c40-f83b-11eb-81c0-fbcc16bf6bdb

Value is just a long string.

What would be the fastest way to find a SINGLE key from localStorage based on only one of the two UUIDs i.e. either UUID1 or UUID2, then obtain the full key string and then use

localStorage.getItem to return it's value

maybe using Object.entries(localStorage)?

a code example would be really appreciated?

local-storage mozilla javascript
2 Answers

The Storage interface has a length property telling you how many items are there, and a key method that gives you the key for item index n. So you can loop through to find the key with a for loop:

let key;
for (let n = 0, len = localStorage.length; n < len; ++n) {
    const thisKey = localStorage.key(n);
    if (thisKey.includes("BLABLABLA")) {
        // found it
        key = thisKey;
        break;
    }
}
if (key) {
    const value localStorage.getItem(key);
    // ...
}

Note that solutions using Object.keys, Object.entries, etc. won't work reliably with all storage keys — for instance, the key "length" won't work properly even though it's just fine to use "length' as a key with getItem and setItem. That's because the Storage interface already defines a property called length (the length of the storage list), so you can't access a stored item keyed by "length' using localStorage.length, you have to localStorage.getItem("length"). Object.keys and Object.entries will leave out those storage entries. (Other than it appears there's a weird bug in Chrome around the "key" key.) The above works reliably with length, key, and other similar keys (but really it's length and key that are the most problematic).

In your particular case, though, you know the key isn't length or key or any of the other things on Storage.prototype, so you could create an array of keys via Object.keys and use find to find the key:

// Read the disclaimers above
const key = Object.keys(localStorage).find(key => key.includes("BLABLABLA"));
if (key) {
    const value localStorage.getItem(key);
    // ...
}

...or use Object.entries to create an array of arrays as charlietfl shows. Just be mindful of the caveat.

user_1572470

Expanding on your Object.entries() concept you can do something like:

// set a demo key/value
localStorage.setItem('foobar', 100);

const [wantedKey, wantedValue] = Object.entries(localStorage).find(([k,v])=> k.startsWith('foo'))



console.log([wantedKey, wantedValue])

Working jsfiddle

user_11759660
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