Purpose This lab converts the previous explanation into a small piece of evidence you created yourself. Do not begin by copying the finished example. Start with the behavior you expect, then make the computer prove or disprove your model.
Your task Launch a small local server, discover its PID/port from another terminal, stop it cleanly, then reproduce an address-in-use error.
Working method 1. Create the smallest clean starting point. 2. Predict the first result in writing. 3. Implement only enough to test that prediction. 4. Run it and capture the result. 5. Add one intentional failure or changed assumption. 6. Diagnose from evidence before editing randomly. 7. Restore the correct behavior. 8. Close the reference and reproduce the important part from memory.
Why this is separate from the concept lesson Reading can create familiarity without recall. The separate lab forces retrieval, execution, and debugging. Those three abilities are what later framework lessons assume when the codebase becomes larger.
Definition of done You have a runnable example, one recorded prediction, one successful result, one controlled failure with diagnosis, and a short explain-back in your own words.
Launch a small local server, discover its PID/port from another terminal, stop it cleanly, then reproduce an address-in-use error.
Run the smallest version first. Capture exact terminal/browser/database output before adding a second concept.
Change one input, ordering, state transition, or configuration assumption. Predict the new output, then run it.
Explain the result in terms of runtime behavior, data flow, identity, or ownership—not “the framework did it”.
Rebuild the example once without looking at the completed version.
# Terminal A
node -e "require('http').createServer((_,res)=>res.end('hello')).listen(4100)"
# Terminal B
Get-NetTCPConnection -LocalPort 4100
Invoke-WebRequest http://localhost:4100Type it, predict it, run it, then change one assumption. The goal is not finishing the snippet; the goal is being able to explain the result.
Deliberately violate one assumption relevant to “Paths, Environment Variables, PATH, and Ports”. Keep the failure small enough that you can identify a single causal change.
Build the smallest example that demonstrates this lesson. Then break one relevant assumption and diagnose it using terminal/DevTools evidence. Finally explain the concept without using a framework name.