Measure repeated timings with honest units
See this course’s project requirements
A before/after optimization record for a supplied local page, with resource-size accounting, reserved image dimensions, fewer blocking resources and repeatable browser measurements.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- Deliver an inventory and measurement table separating bytes, requests, timing, and content checks.
- Produce a delivered-image byte comparison and a preserved-content visual check.
- Verify aspect-ratio reservation and responsive fit, with an appropriate vector/raster source explanation.
- Produce a before/after CSS request-count and preserved-style comparison.
- Retain five actual samples, a correctly calculated median, and an explicit timed-block boundary.
- Deliver a measured, preserve-content before/after packet with performed and unavailable checks separated.
Review and revise
Use these criteria to check your work and choose what to improve.
- The implementation or declared simulation follows the supplied contract and retains inspectable original inputs.
- Normal, boundary and rejected cases are recorded with expected versus observed results.
- The changed case has a correct explanation and does not rely on hidden state.
- The project includes source, outputs, instructions and honest tool, privacy and verification limits.
Want more background?
The idea in everyday life
Serve the supplied folder locally with python3 -m http.server 8765 --bind 127.0.0.1. Compare before.html and after.html. Both show the same original yellow-circle reference graphic and text; only resource packaging and image reservation change.
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
Measure repeated timings with honest units — original worked practice
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
Serve the supplied folder locally with python3 -m http.server 8765 --bind 127.0.0.1. Compare before.html and after.html. Both show the same original yellow-circle reference graphic and text; only resource packaging and image reservation change.
1. Step 1
Activate Measure sorting separately and inspect five samples and the displayed median.
You should see: The page explicitly labels CPU sorting in milliseconds.
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
2. Step 2
Read timing.js: the timer surrounds numeric sorting of 10000 supplied deterministic values.
You should see: The measured block is defined and repeatable.
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
3. Step 3
Write the five samples in ascending order and choose the third as the median.
You should see: The center of five ordered samples is identified.
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
4. Step 4
Repeat on the same page without claiming the smaller SVG caused a different CPU sort result.
You should see: A timed-code record with the measurement boundary explained.
performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation.
What to finish
Retain five actual samples, a correctly calculated median, and an explicit timed-block boundary.
Watch for this
Relabeling a CPU sort timer as whole-page loading or selecting only the fastest sample.
How can I tell I understand it?
Demonstrate the rule: performance.now measures elapsed milliseconds around the chosen code block. These sort timings are not page-load metrics, and repeated samples expose run-to-run variation. Use the supplied variant to distinguish a changed result from a broken implementation.
Quick knowledge check
Answer all 3 questions. Get at least 2 right and the lesson completes automatically.
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Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.
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Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
Source & access notes · checked 2026-10-01
Relevant documented module/API behavior inspected during expansion authoring; actual execution evidence is recorded separately. No grant eligibility is established.
Access: Official page retrieved with the web reader on 2026-10-01. Documentation reading does not certify execution in every native tool or browser.
Reuse: Original local practice files, fictional data, worked examples and questions. Concepts paraphrased and linked; source exercises are not copied.
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