Promise.race and Promise.allSettled in Node.js - Performance & Optimization

Performance: Promise.race and Promise.allSettled

MEDIUM IMPACT

This concept affects how asynchronous operations impact page responsiveness and resource usage during concurrent tasks.

Handling multiple asynchronous tasks and responding as soon as one finishes

Node.js

await Promise.race([task1(), task2(), task3()]); // resolves or rejects as soon as one task settles

Returns as soon as the first promise settles, improving responsiveness and reducing wait time.

📈 Performance Gainreduces blocking time, improves INP by responding faster

Handling multiple asynchronous tasks and responding as soon as one finishes

Node.js

await Promise.allSettled([task1(), task2(), task3()]); // waits for all tasks to finish

This waits for all tasks to complete even if you only need the first result, delaying response time.

📉 Performance Costblocks interaction until all promises settle, increasing INP

Performance Comparison

Pattern	Async Wait Time	UI Responsiveness	Resource Usage	Verdict
Promise.allSettled for first result	Long (waits all)	Low (delayed)	High (all tasks run fully)	[X] Bad
Promise.race for first result	Short (first settles)	High (fast response)	Moderate (tasks still run)	[OK] Good
Promise.all for all success	Medium (waits all success)	Medium (may reject early)	High (may retry)	[!] OK
Promise.allSettled for all results	Long (waits all)	High (stable UI)	Moderate (no retries)	[OK] Good

Rendering Pipeline

Async promise handling affects the JavaScript execution and event loop stages, influencing when UI updates can occur.

→JavaScript Execution

→Event Loop

→Rendering

⚠️ BottleneckJavaScript Execution blocking UI updates while waiting for promises

Core Web Vital Affected

INP

This concept affects how asynchronous operations impact page responsiveness and resource usage during concurrent tasks.

Optimization Tips

1Use Promise.race to improve responsiveness by reacting to the first settled promise.

2Use Promise.allSettled to get results from all promises without early rejection.

3Avoid Promise.all if you need full results and want to prevent retries or UI flicker.

Performance Quiz - 3 Questions

Which Promise method returns as soon as the first promise settles, improving responsiveness?

A Promise.all

B Promise.allSettled

C Promise.race

D Promise.resolve

DevTools: Performance

How to check: Record a performance profile while running async tasks; look at the JavaScript call stacks and event loop delays.

What to look for: Check for long blocking times in JS execution and delayed UI updates indicating slow promise resolution.