Adding data to existing local storage? JavaScript

Question

I have been writing some code that adds an item to a local storage array but have hit an issue where the array is not updated. As localStorage does not allow arrays, I have been converting to a string.

function addItem(add_item) {

    if (localStorage.getItem("list_items") === null) {
        localStorage.setItem("list_items", "");
    }
    else {
        "Something has gone horribly wrong!"
    }

    // Check if item is already added
    if(existingEntries == null) existingEntries = [];
    else {
        existingEntries = JSON.parse(localStorage.getItem("list_items"));
    }

    // Set entry to the currently selected item
    var entry = add_item;

    // Check if item is in string
    var exists = existingEntries.includes(entry);

    // Add item if it's not already in the array
    if (exists == false) {
        existingEntries.push(entry);
        localStorage.setItem("list_items", JSON.stringify(existingEntries));
    }
}

For some reason, the local storage is not being updated with the new value added on. Any ideas as to why? Thank you in advance.

@DamienGold that would overwrite what is already there and not allow storing array — charlietfl
– charlietfl, Commented Apr 7, 2018 at 23:50

charlietfl · Accepted Answer · 2018-04-08 00:00:13Z

2

You have over complicated it.

Simplify this down to something like:

function addItem(add_item) {

  // parse existing storage key or string representation of empty array
  var existingEntries = JSON.parse(localStorage.getItem("list_items") || '[]');

  // Add item if it's not already in the array, then store array again
  if (!existingEntries.includes(add_item)) {
    existingEntries.push(add_item);
    localStorage.setItem("list_items", JSON.stringify(existingEntries));
  }else{
     // or tell user it's already there
     console.log(add_item + ' already exists')
  }
}

edited Apr 8, 2018 at 0:00

answered Apr 7, 2018 at 23:49

charlietfl

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2 Comments

The Fat Fish Over a year ago

So to delete I would do: if (existingEntries.includes(add_item)) { existingEntries.splice(add_item); localStorage.setItem("list_items", JSON.stringify(existingEntries)); }else{ }

charlietfl Over a year ago

you need to get the index of the item to use splice()

Damien · Accepted Answer · 2018-04-07 23:42:56Z

0

If your localstorage has data with a key 'list_items', localStorage.setItem("list_items", "my new data"); will overwrite the old data.

answered Apr 7, 2018 at 23:42

Damien

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