JavaScript, How to concat objects into arrays in LocalStorage?

Question

I am currently working on a project using geolocation. Every 30 seconds, the current location was retrieved from GeoLocation and saved to LocalStorage. I want to concat the stored objects into an array. How do I do this?

    const lastIndex = localStorage.getItem("lastIndex");
    const endLocation = JSON.parse(localStorage.getItem("location"+lastIndex));

    let map = [];

    for(let i = 0 ; i <= lastIndex ; i++) {
        map.concat(JSON.stringify(localStorage.getItem("location"+i)));
        localStorage.removeItem("location"+i);
    };

This is my code.

In other words, I want to return a new object by putting the location object through the map array.

For example - map = [{"lng" : "37.12345", "lat" : "13.12345", "timestamp" : "12141251121212"},

{"lng" : "37.12345", "lat" : "13.12345", "timestamp" : "12141251121212"},

{"lng" : "37.12345", "lat" : "13.12345", "timestamp" : "12141251121212"} ]

But what comes out is null, what should I do?

T.J. Crowder · Accepted Answer · 2021-05-23 13:17:08Z

1

concat returns the new array, it doesn't modify the array you call it on. You aren't using that return value, so you don't see the combined result.

Also, since concat returns a new array each time, it's probably not a great choice for this. Just use push:

const map = [];
for (let i = 0; i <= lastIndex; ++i) {
    const key = "location" + i;
    map.push(JSON.parse(localStorage.getItem(key));
    localStorage.removeItem(key);
}
// Use `map` here...

Note that you were using JSON.stringify where you wanted JSON.parse.

answered May 23, 2021 at 13:17

T.J. Crowder

1.1m201 gold badges2k silver badges2k bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

JavaScript, How to concat objects into arrays in LocalStorage?

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related