Performance auditing with Lighthouse in Astro - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Lighthouse in the context of web development?

Lighthouse is a tool that checks how well a website performs, how accessible it is, and how good its SEO is. It gives a report with scores and suggestions to improve.

beginner

How do you run a Lighthouse audit for an Astro project?

You open Chrome DevTools, go to the Lighthouse tab, select the categories you want, and click 'Generate report'. You can also run Lighthouse from the command line.

beginner

What are the main categories Lighthouse evaluates?

Lighthouse checks Performance, Accessibility, Best Practices, SEO, and Progressive Web App (PWA) features.

intermediate

Why is performance auditing important for Astro projects?

Because Astro builds fast websites, auditing helps find any slow parts or issues so you can fix them and keep the site quick and smooth for users.

intermediate

Name one common performance issue Lighthouse might find in an Astro site.

Lighthouse might find unused JavaScript or large images that slow down loading times.

Which tool is used to audit website performance and accessibility?

A ESLint

B Lighthouse

C Babel

D Webpack

Lighthouse is the tool designed to audit website performance, accessibility, SEO, and more.

Where can you find the Lighthouse tool in Chrome?

A Console tab

B Settings > Extensions

C Network tab

D DevTools > Lighthouse tab

Lighthouse is integrated into Chrome DevTools under the Lighthouse tab.

Which of these is NOT a Lighthouse audit category?

A Database Optimization

B Accessibility

C Performance

D SEO

Database Optimization is not a Lighthouse audit category.

Why should you fix issues found by Lighthouse in an Astro project?

A To increase server costs

B To add more animations

C To improve website speed and user experience

D To make the code longer

Fixing issues improves speed and user experience, which is the goal of performance auditing.

What is a common cause of slow loading times found by Lighthouse?

A Unused JavaScript

B Too many comments in code

C Using CSS variables

D Small image sizes

Unused JavaScript can slow down loading times and is often flagged by Lighthouse.

Explain how you would use Lighthouse to improve an Astro website's performance.

Think about the steps from running the tool to applying fixes.

Describe the main categories Lighthouse audits and why each is important.

Consider what each category helps improve on a website.

Practice

1. What is the main purpose of using Lighthouse with an Astro site?

easy

A. To check and improve the site's performance and usability

B. To write new Astro components automatically

C. To deploy the Astro site to a server

D. To convert Astro code into plain HTML

Solution

1. Step 1: Understand Lighthouse's role

   Lighthouse is a tool designed to analyze websites and provide reports on performance, accessibility, SEO, and best practices.

2. Step 2: Relate to Astro site improvement

   Using Lighthouse on an Astro site helps find ways to improve speed and usability, making the site better for users.

3. Final Answer:

   To check and improve the site's performance and usability -> Option A

4. Quick Check:

   Lighthouse purpose = Performance & usability check [OK]

Hint: Lighthouse audits site quality, not code writing or deployment [OK]

Common Mistakes:

• Thinking Lighthouse writes code
• Confusing Lighthouse with deployment tools
• Assuming Lighthouse converts code formats

2. Which command correctly runs Lighthouse from the command line for the URL https://example.com?

easy

A. start lighthouse --url https://example.com

B. run lighthouse https://example.com

C. lighthouse https://example.com

D. lighthouse run https://example.com

Solution

1. Step 1: Recall Lighthouse CLI syntax

   The basic command to run Lighthouse is simply lighthouse followed by the URL.

2. Step 2: Match the correct syntax

   lighthouse https://example.com matches the correct syntax: lighthouse https://example.com. Other options add unnecessary words or flags.

3. Final Answer:

   lighthouse https://example.com -> Option C

4. Quick Check:

   Correct CLI syntax = lighthouse URL [OK]

Hint: Use just 'lighthouse' plus URL to run audit [OK]

Common Mistakes:

• Adding extra words like 'run' or 'start'
• Using incorrect flags or options
• Confusing command order

3. After running Lighthouse on your Astro site, you see a low score in the 'Performance' category. What is the most likely cause?

medium

A. The site is missing a favicon

B. The site uses too many Astro components

C. The site has no SEO metadata

D. The site has large images and slow loading scripts

Solution

1. Step 1: Understand what affects Performance score

   Performance issues usually come from slow loading resources like large images or heavy scripts.

2. Step 2: Eliminate unrelated options

   SEO metadata and favicon affect SEO or appearance, not performance. Number of Astro components alone doesn't cause low performance.

3. Final Answer:

   The site has large images and slow loading scripts -> Option D

4. Quick Check:

   Performance issues = large images or slow scripts [OK]

Hint: Performance drops mainly due to heavy resources [OK]

Common Mistakes:

• Confusing SEO issues with performance
• Blaming Astro components count directly
• Ignoring resource sizes

4. You ran Lighthouse but the report shows no data and an error message. What is the most likely mistake?

medium

A. You ran Lighthouse without specifying a URL

B. You ran Lighthouse on a local file without a server

C. You forgot to install Astro globally

D. You used an outdated version of Node.js

Solution

1. Step 1: Identify why Lighthouse shows no data

   Lighthouse needs a live URL to audit. Running it on a local file without a server means no data can be fetched.

2. Step 2: Check other options

   Not specifying a URL would cause a command error, not a no data report. Astro installation or Node.js version do not directly cause this error.

3. Final Answer:

   You ran Lighthouse on a local file without a server -> Option B

4. Quick Check:

   Lighthouse needs live URL, not local file [OK]

Hint: Always run Lighthouse on a live server URL, not local files [OK]

Common Mistakes:

• Running Lighthouse on local files without server
• Ignoring error messages about URL
• Assuming Astro install affects Lighthouse

5. You want to improve your Astro site's Lighthouse performance score. Which combination of actions is best?

hard

A. Optimize images, lazy-load components, and reduce JavaScript size

B. Add more Astro components and increase CSS animations

C. Remove all images and use only text content

D. Disable Lighthouse caching and run audits repeatedly

Solution

1. Step 1: Identify actions that improve performance

   Optimizing images reduces load time, lazy-loading defers offscreen content, and reducing JS size speeds up scripts.

2. Step 2: Evaluate other options

   Adding components or animations can slow performance. Removing all images is impractical. Disabling caching doesn't improve site speed.

3. Final Answer:

   Optimize images, lazy-load components, and reduce JavaScript size -> Option A

4. Quick Check:

   Best performance = optimize images + lazy-load + reduce JS [OK]

Hint: Focus on image size, lazy loading, and JS reduction [OK]

Common Mistakes:

• Thinking more components always help
• Removing images entirely
• Misunderstanding caching effects