Summary - Local storage

JavaScript course · Intermediate · Lesson 48/134

Build an app that saves and restores a dark-mode preference using localStorage and JSON.

Summary - Local storage

In this group you learned to store data with localStorage and sessionStorage. localStorage is persistent; sessionStorage is cleared when the tab closes. Both store only text; you turn arrays and objects into text with join and split and read them back.

For clearing, removeItem deletes one key and clear deletes all. To react to changes in another tab, you listen for the storage event. Now you will build an app that brings these together.

Exercise Save and read a dark-mode preference

Save the value 'dark' under the 'theme' key with setItem. Then read it with getItem; set isDark to true if the value is 'dark', otherwise false.

Show example solution

localStorage.setItem('theme', 'dark');
const saved = localStorage.getItem('theme');
const isDark = saved === 'dark';

Exercise Delete the preference and read it back

Delete the 'theme' key with removeItem. Then read it again with getItem and assign the result to a theme variable.

Show example solution

localStorage.removeItem('theme');
const theme = localStorage.getItem('theme');

Test yourself

Which storage type survives a browser restart?
```
localStorage.setItem('a', '1');
sessionStorage.setItem('b', '2');
```
- sessionStorage
- localStorage
- windowStorage
- tempStorage
Show answer

localStorage — Correct! localStorage survives a browser restart.
Match all the methods

setItem(k, v)

Saves the value
getItem(k)

Reads the value
removeItem(k)

Deletes one key
clear()

Deletes everything

All lessons in Intermediate

1 Arrow functions

2 Scope

3 Closures

Summary - Local storage