[Sketchnote] Web Storage APIs: How Browsers Store Data

November 29th, 2020

(2-minute read)

Browsers have two built-in ways to store data: sessionStorage and localStorage.

sessionStorage

• Data stored there is cleared when the page session ends (i.e., the browser tab/window closes).
• Each tab has its own sessionStorage object, independent from the one in other tabs.

localStorage

• Data stored there has no expiration time.
  • Exception: If you're in a private tab, then localStorage is cleared when the last private tab is closed.
• Storage object is specific to the protocol. (HTTP object is separate from HTTPS.)

Common API

sessionStorage and localStorage both implement the Storage interface.

Both objects contain a key-value store, which is where data is kept. The keys and values are both type DOMString.

Properties

• .length - The number of entries in the Storage object's key-value store.

  javascript

  const numEntries = sessionStorage.length

Methods

• .setItem(key, value) - Adds the key-value pair to the store.

  javascript

  localStorage.setItem("key", "value")

• .getItem(key) - Retrieves the value for the specified key. (Returns null if the key doesn't exist.)

  javascript

  const username = sessionStorage.getItem("key")

• .removeItem(key) - Removes the key-value pair for the specified key. (If the key doesn't exist, nothing happens.)

  javascript

  sessionStorage.removeItem("key")

• .clear() - Removes all key-value pairs from the store.

  javascript

  localStorage.clear()

Additional Resources

• Window.sessionStorage
• Window.localStorage