LocalStorage
LocalStorage allows you to store key-value pairs in the user browser with no expiration date.
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📋 Copy Safe LocalStorage Wrapper & Quota Guard Snippet
// Safe localStorage Wrapper with Quota Guard
const Storage = {
get(key, fallback = null) {
try {
const item = localStorage.getItem(key);
return item ? JSON.parse(item) : fallback;
} catch {
return fallback;
}
},
set(key, value) {
try {
localStorage.setItem(key, JSON.stringify(value));
return true;
} catch (e) {
console.warn("Storage quota exceeded", e);
return false;
}
}
};⚠️ 5 Fatal Traps & JavaScript Pitfalls
Trap #1: Storing Sensitive Tokens in localStorage (XSS Vulnerability)
Any third-party script or XSS vulnerability on your origin can read
localStorage. Never store authentication tokens or credentials in localStorage; use HTTP-only, secure cookies.Trap #2: QuotaExceededError Crash (~5MB Limit)
Attempting to store more than ~5MB throws an uncaught
QuotaExceededError that crashes scripts. Always wrap localStorage.setItem() in a try...catch.Trap #3: Synchronous Main Thread Blocking I/O
localStorage reads and writes synchronously from disk on the main browser thread. Storing massive multi-megabyte strings causes noticeable frame drops and UI stutter.
Trap #4: Missing Keys Returning null vs undefined
localStorage.getItem("missing") returns null, not undefined. Default parameters (const val = localStorage.getItem(...) || default) should account for null.Trap #5: Private Browsing and Cookie-Blocked Exceptions
In Safari private browsing or when third-party cookies are blocked, merely accessing
window.localStorage can throw a SecurityError.💬 Frequently Asked Questions
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