TypeError: Cannot read properties of null (reading 'addEventListener')
TypeError: null is not an object (evaluating 'x.name')

You’re trying to access a property or call a method on null. The variable exists but has no value.

Fix 1: DOM Element Not Found

// ❌ Element doesn't exist (yet)
const btn = document.getElementById('submit');
btn.addEventListener('click', handler);  // 💥 btn is null

// ✅ Check if element exists
const btn = document.getElementById('submit');
if (btn) {
    btn.addEventListener('click', handler);
}

// ✅ Or wait for DOM to load
document.addEventListener('DOMContentLoaded', () => {
    document.getElementById('submit').addEventListener('click', handler);
});

Fix 2: Script Loaded Before HTML

<!-- ❌ Script runs before the element exists -->
<script src="app.js"></script>
<button id="submit">Click</button>

<!-- ✅ Put script at the end or use defer -->
<button id="submit">Click</button>
<script src="app.js"></script>

<!-- Or use defer -->
<script defer src="app.js"></script>

Fix 3: API Returned Null

// ❌ Assuming API always returns data
const user = await fetchUser(id);
console.log(user.name);  // 💥 If user is null

// ✅ Handle null response
const user = await fetchUser(id);
if (!user) {
    console.log('User not found');
    return;
}
console.log(user.name);

Fix 4: React — Ref Not Attached Yet

// ❌ Accessing ref before component mounts
const inputRef = useRef(null);
inputRef.current.focus();  // 💥 null on first render

// ✅ Use useEffect
useEffect(() => {
    inputRef.current?.focus();
}, []);

Fix 5: Optional Chaining

// ❌ Deep property access
const city = user.address.city;  // 💥 If address is null

// ✅ Optional chaining
const city = user?.address?.city ?? 'Unknown';

Fix 6: querySelector Returns Null

// ❌ Selector doesn't match anything
const el = document.querySelector('.nonexistent');
el.style.color = 'red';  // 💥 null

// ✅ Guard against null
const el = document.querySelector('.nonexistent');
if (el) el.style.color = 'red';

Related resources

• Cannot read properties of undefined fix
• React cannot read null fix
• TypeScript object is possibly undefined fix

Related: JavaScript Array Methods Cheat Sheet · React Interview Questions · React White Screen Blank Page Fix