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JavaScript and interaction · Lesson 03 / 14

Decisions with clear boundaries

A number seems acceptable until input is empty, fractional or too large.

Learning paths14 min

Let's discover together

  1. 1

    If executes a branch based on a condition; else handles the other path. Compare boundaries explicitly: n >= 1 && n <= 120. && requires both conditions; || accepts at least one.

  2. 2

    Values can be used as conditions, but truthy does not mean valid. The string "0" is truthy even though zero minutes is not accepted here. Trim whitespace, reject empty input, convert and check the number.

  3. 3

    Number.isInteger(n) rejects fractions, NaN and Infinity. The project accepts only decimal digits for duration and the range 1–120; this also rejects notation such as "1e2". State the product rule explicitly.

  4. 4

    Test below, inside and above the boundary: 0, 1, 120 and 121, plus empty input and 1.5. Testing 15 alone does not reveal boundary behavior.

From the example to your own interaction

Download this activity kit, extract it and open index.html in a browser. Edit lesson.js, save and reload. You do not need Node or packages. README explains local HTTP when needed.

The demonstration uses supplied JavaScript. It does not execute your editor code. Download your edit separately to test in the local kit.

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Try the project we will build

Small mission planner

Create, complete and review a study plan using fictional data. Missions stay only in this page’s memory and disappear on reload.

Use a short title without personal data and whole minutes from 1 to 120. Up to 20 missions.

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    Suggestion lab

    Scenarios are simulated in this browser by default. No suggestion request is sent and your plan is not replaced.

    Available in the kit opened at http://127.0.0.1:8768. See README; no external account is needed.

      This JSON contains only missions, not your code. The demonstration does not import files or synchronize devices. Download edited JavaScript from the lesson file workspace.

      Official links and next step

      ✦
      YOUR MISSION

      Use if and explicit conditions to accept only whole minutes from 1 to 120.

      Now it's your turn

      Discovery workshop

      Think before running

      Duration must be a whole number from 1 through 120.
      Build your answers and check when you are ready.
      A moment to understand

      Is a truthy string always a valid duration?

      I need a hint

      Predict the result, run your file and explain the difference.

      Loading your journey…

      Take it with you

      Add an invalid case and explain which check rejects it. Temporarily change <= to < and find the failing test.

      At your own pace

      My files and GitHub

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