JavaScript & DOM ⚡ Recently updatedUpdated on Jun 30, 2026 — this content may still be evolving.

JavaScript DOM: Mock Interview (45 Minutes)

Use with a friend. Switch interviewer/candidate roles after.

Rules:

• Candidate answers out loud
• Interviewer asks 2+ follow-ups per question
• Section 4 is live coding

Section 1: Warm-up (5 min)

1. “Describe a vanilla JS project or feature you’ve built.”
2. “Why learn DOM if frameworks exist?”
3. “What’s the hardest DOM bug you’ve debugged?”

Section 2: DOM Fundamentals (10 min)

1. “How do you select elements in the DOM?”
   • Follow-up: “querySelectorAll returns what type?”
2. “Difference between textContent and innerHTML?”
   • Follow-up: “Security concern with innerHTML?”
3. “How do you create and append a new list item?”

Section 3: Events (8 min)

1. “Explain event bubbling.”
   • Follow-up: “What is event capturing?”
2. “What is event delegation? When do you use it?”
   • Follow-up: “target vs currentTarget?”
3. “Difference between preventDefault and stopPropagation?”

Section 4: Live Coding (12 min)

Pick ONE:

Option A: Todo item add + delete

“Build HTML structure and JS to add todos and delete them. Use event delegation for delete.”

Evaluate: preventDefault or button type, createElement, delegation on parent.

Option B: Filter list

“Given a list of names in HTML, filter them as user types in a search box.”

Option C: Fetch and display

“Fetch posts from JSONPlaceholder and render as a list. Handle loading and error.”

Follow-ups:

• “How would you persist todos?”
• “How would you debounce the search?”

Section 5: Forms & APIs (5 min)

1. “How do you submit a form without page reload?”
2. “How do you read form data in JS?”
3. “Walk through a fetch call — what can go wrong?”

Section 6: Project & Advanced (5 min)

Pick 2:

1. “How would you implement a modal?”
2. “localStorage vs sessionStorage?”
3. “How to lazy-load images?”
4. “1000 list items — performance concerns?”

Project connection:

• “Open your project — show me where you manipulate the DOM.”
• “What would you refactor?”

Evaluation Rubric

Debrief (5 min)

Homework: Complete 2 challenges from mini-dom-challenges.md you haven’t built yet. Redo Section 4 in under 10 minutes.