Question 1

How would you use the Page Visibility API to pause a setInterval-based poller when a user switches to a different browser tab?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript browser-API interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result below was actually run against a real jsdom document on Node.js v24.19.0 — the printed output is real, captured output, not illustrative sample text. ## 1. Why This Even Matters — A Story First Picture a delivery app polling a restaurant every fe

Question 2

Why would you use performance.now() instead of Date.now() to measure how long a function takes to run?

Accepted Answer

**Target Audience:** Engineers preparing for JavaScript performance-measurement interview questions. **Difficulty:** Medium > **How to read this doc:** Concepts are explained in plain language first, then tagged with 📌 Interview term:. Every result below was actually run on Node.js v24.19.0 — the printed output is real, captured output, not illustrative sample text. ## 1. Why This Even Matters — A Story First Imagine timing a race two different ways. One timer is a wall clock th

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Easy

How would you use the Page Visibility API to pause a setInterval-based poller when a user switches to a different browser tab?

Why would you use performance.now() instead of Date.now() to measure how long a function takes to run?