Build a coding exercises app for beginners, and know why it can't run any code you type
Anticode can build a coding exercises app for beginners, with one honest limit up front: the app is not allowed to run code a learner types. Its sandbox refuses code built from strings, which running typed code needs. That still leaves plenty: reading code, predicting output, spotting bugs and ordering lines, all checked in the browser. For writing and running real programs, a learner needs a proper code environment.
Why typed code can't run here
To run what a learner types, a page has to turn their text into code at run time, with eval, new Function or a similar route. Anticode's code gate checks every app before it's shown or published and rejects those calls, because code built from strings is a classic way to smuggle unchecked behaviour into a page. There's also no network, so the app can't send code to a server that runs Python, Java or anything else. The result is a firm rule: no exercise in the app executes the learner's code.
That's a real limitation, and it's why this is a partial fit. If your goal is "write a function and see the tests pass", use an online code playground or a local editor.
Exercise types that work without running code
Many programming teachers argue that beginners need far more practice reading code than they usually get, and these formats suit that well. Each is checked by comparing the learner's choice with an answer written into the exercise.
| Format | What the learner does | How it's checked |
|---|---|---|
| Predict the output | Reads a short snippet and types what it logs | Exact match against the expected output, with whitespace ignored |
| Trace the variables | Fills in a table of a variable's value after each line | Each cell compared with the answer |
| Spot the bug | Clicks the line that's wrong, then picks the fix | Line number and choice compared |
| Parsons problems | Drags scrambled lines into the right order and indentation | Order compared, allowing known valid alternatives |
| Fill the blank | Types a missing operator, keyword or value | Match against a list of accepted answers |
| Multiple choice | "Which loop prints 1 to 10?" | Choice compared |
Write accepted alternatives into each exercise. i++ and i += 1 are both right; an app that accepts only one teaches the wrong lesson.
Describe it to Anticode
"A coding exercises app for complete beginners learning JavaScript. Units: variables, conditions, loops, arrays, functions, objects. Each unit has ten exercises mixing predict the output, trace the variables, spot the bug, Parsons problems and fill the blank. Code shown with syntax highlighting in a readable monospace font. A hint button with two levels, and an explanation after each answer. Progress per unit saved in this browser, with a review mode for exercises answered wrongly. Never run the learner's input as code; check answers against expected answers written into each exercise."
Write the first few exercises yourself and give them in the description, so the app's style follows yours. Then ask for more in the same style and check every answer key carefully: a wrong key in a teaching app does real harm.
Where it's useful
- A teacher's warm-up: ten predict-the-output questions at the start of a lesson, on the classroom screen.
- Homework between lessons for learners who don't yet have a coding setup at home.
- Interview preparation focused on reading unfamiliar code quickly.
- A bootcamp's pre-course check, with the score sent through a contact form if you ask for one.
Limits
- No running code, so no free-form programming tasks and no test suites.
- JavaScript-flavoured reading only in practice; other languages can be shown as text, but nothing about them is executed either.
- No accounts or class dashboard. Progress stays in each learner's browser.
- No AI feedback on answers inside the app; explanations are written in advance.
For quizzes on any subject, see the practice test maker; for step-by-step lessons, the interactive lesson page. Learners curious about how the apps themselves are built can read about Anticode's app sandbox.
Questions people ask
Can a coding exercises app built with Anticode run my students' code?
No. The app sandbox rejects code built from strings, so typed code is never run. Exercises are checked against written answers.
Can it teach Python?
It can show Python snippets for reading and prediction exercises, but nothing is executed. For writing Python, use a Python environment.
How are answers checked, then?
Against answers written into each exercise: expected output, the right line, the right order, or a list of accepted values.