DOM API Polyfills and Implementations Questions

Covers implementing and reasoning about Document Object Model methods and utilities that browsers provide. Candidates should be able to recreate common query and traversal functions such as document.getElementsByClassName, document.querySelector, Element prototype closest, and related helpers. Expect questions about tree structure and traversal algorithms, live versus static node list behavior, event delegation patterns, and practical utilities for traversing and searching the Document Object Model efficiently. Interviewers may probe performance implications of different query strategies, when and how to cache query results, memory and update cost trade offs, and how to implement robust polyfills that behave like native methods in typical cases.