Render clear success and error states
See this course’s project requirements
A keyboard-usable local workshop calculator with clear validation, correct totals, and an eight-case test record.
Keep your working files in your own notebook or software. Save a private description, checklist, and work link in My Proof.
What to include
- Two-input state trace.
- Deliberate type conversion and blank handling.
- Isolated tested calculation.
- Shared submit handler for pointer and keyboard.
- Clear feedback and eight-case test record.
Review and revise
Use these criteria to check your work and choose what to improve.
- Totals match the stated rule.
- Invalid input never shows a current total.
- Keyboard and pointer paths work consistently.
- Tests and limitations are accurately reported.
Want more background?
The idea in everyday life
Make a small fictional workshop calculator respond reliably to user input.
A result is meaningful only when its validity is clear.
Render clear success and error states — guided practice
Clear stale results and explain invalid inputs in text.
Save workshop-calculator.html and open it locally in a browser; open the same file in a text editor. It is a complete original worked program. The rule is 8 units per seat, 1–6 whole seats, plus one optional 5-unit group pack. Nothing is sent or bought. Restore the supplied file before each lesson’s code variation.
1. Create a success
Calculate 2 seats and no pack.
You should see: 16 units appears.
Start with visible old content to test error replacement.
2. Create an invalid case
Enter 7 and calculate.
You should see: Error asks for 1–6 whole seats; the old 16 disappears.
An old successful total must not accompany an invalid current input.
3. Inspect attributes
Use the console to read aria-invalid on seats.
document.querySelector("#seats").getAttribute("aria-invalid")You should see: It is true after the invalid attempt.
Text and semantic state support more users.
4. Recover
Enter 6 and calculate.
You should see: Error clears, aria-invalid is false and total is 48.
A successful correction should fully replace error state.
What to finish
A success/error/recovery record.
Watch for this
Using color alone to convey errors or leaving a prior total visible.
How can I tell I understand it?
Complete the changed case, explain your result, and pass the three application checks.
Quick knowledge check
Answer all 3 questions. Get at least 2 right and the lesson completes automatically.
You’ll get an explanation for each answer. Signed in? Your results save to your account.
Pass the check. We’ll save the progress.
Answer all 3 questions above and get at least 2 right. You can review the explanations and try again.
Go to the knowledge checkOptional course overview video · same video as Lesson 1
JavaScript DOM Crash Course - Part 1
From Traversy Media. Watch here or open it on YouTube .
Optional course overview. Follow the written steps below at your own pace.Tools, templates, and lesson sources
Tools and templates
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Sources and further reading
Explore the references behind this lesson.
Source & access notes · checked 2026-09-12
Opened and inspected on 2026-09-12: Element selection and text updates.
Access: Free public web page; no paid enrollment required.
Reuse: Public reference; link only. LifeStarter prose, exercises and files are independently authored.
Source & access notes · checked 2026-09-12
Opened and inspected on 2026-09-12: Input constraints and useful errors.
Access: Free public web page; no paid enrollment required.
Reuse: Public reference; link only. LifeStarter prose, exercises and files are independently authored.
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