Bugs
TypeError: Cannot Read Properties of Undefined in JavaScript
This is one of the most common JavaScript errors. It occurs when code tries to access a property on a value that is undefined or null.
❌ Code Causing TypeError
async function displayUser(userId) {
const user = await fetchUser(userId);
// fetchUser returns undefined if not found
console.log(user.name); // TypeError if user is undefined!
console.log(user.address.city); // Nested crash risk
}✅ Fixed with Optional Chaining
async function displayUser(userId) {
const user = await fetchUser(userId);
if (!user) { console.log('User not found'); return; }
console.log(user.name);
console.log(user?.address?.city ?? 'No city on record');
}💡
Pro tip: Use optional chaining (?.) to safely access nested properties. Use ?? to provide fallback values for null/undefined.
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