Browser & Web Performance · Junior · Question 26 of 75

Why does heavy JavaScript make a page feel slow even after it has loaded?

1Browsers download JavaScript again on every click
2JavaScript always runs on the GPU and competes with images
✓Correct answer: JavaScript runs on the main thread, which also handles input and rendering, so long scripts delay both

Explanation

Splitting work into smaller tasks, deferring non-critical code and moving heavy computation to workers keeps the main thread free.

Further reading

Test yourself

Take the Browser & Web Performance · Junior quiz: questions and options are shuffled, and you get a review of your mistakes at the end.