window.localStorage offers a way of persisting data across sessions and is specific to that page that created the entries in the storage.


localStorage items are stored as key-value pairs both being valid utf-8 strings(valid JSON).

1. Store an item

To store an item, we convert the item into a JSON valid string, then set a key to uniquely identify this item for retrieval later

const item = { id: 1, name: 'UVSensor' }
// storing the item:
window.localStorage.setItem('sensor', JSON.stringify(item))

From the above snippet, sensor is the key, and JSON.stringify(item) is the value with which the key will be associated with.

2. Retrieve an item

To retrieve an item:

// ...possible portions of code ommitted
const itemJson = window.localStorage.getItem('sensor')
// Parse the item into regular JSON
  let item = JSON.parse(itemJson)
  return item
To retrieve an item from `localStorage`, we use the key to which the element was set to.

3. Removing an Item

The syntax for removing an item is as follows:


localStorage is available off the global window object, hence calling window.localStorage is unnecessary.

4. Remove all items

The syntax for removing all items is as follows:

window.localStorage.clear(); // removes all the items

For a full article on window.localStorage check out this article on Web storage API

Things to note

  1. Never use localStorage to store sensitive data
  2. Use a persistent means, a database to store information, if a user clears their browser cache all the information stored shall be lost.