Rullst AcademyRullst Academy/Lesson
JavaScript and interaction · Lesson 02 / 14

Values with names

A mission has a title, duration and completion flag. Each value has a role.

Learning paths14 min

Let's discover together

  1. 1

    A string represents text, number represents numbers and boolean uses true/false. Quotes matter: "15" is text, 15 is a number. null can represent deliberate absence; undefined appears, for example, when a function returns no value.

  2. 2

    Use const when you do not intend to reassign a variable and let when reassignment is needed. Const does not freeze an object: its properties can change. Prefer names that explain the value, such as minutes, and consistency throughout the project.

  3. 3

    The + operator adds numbers but also concatenates strings. "2" + 3 produces "23"; Number("2") + 3 produces 5. Do not convert without checking input: Number("") is zero and Number("abc") produces NaN.

  4. 4

    Use === for equality without type coercion: 15 === "15" is false. Assignment uses =, not ===. Before changing a result, inspect typeof and record the value being used.

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.

My files and GitHub
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.

Missions in the plan
0
Minutes across all missions
0
Completed missions
0

No missions in this filter. Add one or choose another filter.

    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

      Distinguish strings, numbers, booleans and assignment with let/const.

      Now it's your turn

      Discovery workshop

      Think before running

      const mission = {minutes: 15}; mission.minutes = 20;
      Build your answers and check when you are ready.
      A moment to understand

      Is 15 === "15" true?

      I need a hint

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

      Loading your journey…

      Take it with you

      Make three predictions using +, Number and ===. Run and record value and type, including one that surprised you.

      At your own pace

      My files and GitHub

      Every lesson can become your own record: code, notes or a practice plan. Saving a file to GitHub is optional and does not change your XP.

      Student guide

      The editor and downloads open when this lesson is available to your account. Check access below or return to the track map.

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      Rullstpetbot

      AI can make mistakes. Check the lesson material.