JavaScript Local Storage

Web storage lets you save small pieces of data in the visitor’s browser. There are two kinds.

Storage	Lives until
localStorage	Deleted by the user or by your code. It stays after closing the browser
sessionStorage	The tab is closed

localStorage.setItem("theme", "dark");

console.log(localStorage.getItem("theme"));
console.log(localStorage.getItem("missing"));

localStorage.removeItem("theme");
console.log(localStorage.getItem("theme"));

• setItem(key, value) saves.
• getItem(key) reads, and gives null if there is no such key.
• removeItem(key) deletes one, clear() deletes everything.

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Store objects and arrays

Storage keeps only strings. Convert objects with JSON.

const settings = { theme: "dark", fontSize: 18 };

localStorage.setItem("settings", JSON.stringify(settings));

const saved = JSON.parse(localStorage.getItem("settings"));
console.log(saved.fontSize);

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Example: remember a visitor name

let name = localStorage.getItem("visitorName");

if (!name) {
  name = prompt("What is your name?");
  localStorage.setItem("visitorName", name);
}
console.log("Welcome " + name);

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Summary

• localStorage stays, sessionStorage ends with the tab.
• Use setItem, getItem, removeItem.
• Use JSON.stringify and JSON.parse for objects.
• Next: JavaScript Modules.

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Exercises & Assignments
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