Calculator Bugs

Work on this exercise locally

This web app is a reference guide — you can read instructions, browse starter code, and view tests here. To actually complete the exercise, you need to work in your local development environment.

1Clone the repo: git clone https://github.com/weihaoqu/program-analysis-bootcamp-student

2Edit the starter file in your editor (VS Code, Vim, etc.) — replace failwith "TODO" with your implementation.

3Run the tests: dune runtest modules/module1-foundations/exercises/calculator-bugs

3. Exercise 1: Calculator Bugs

Goal: Find 8 bugs in a JavaScript calculator using static analysis (ESLint) and dynamic analysis (a test suite), then compare what each approach catches.

Time: ~30 minutes

Files:

File	Purpose
`exercises/calculator-bugs/starter/calculator.js`	The buggy calculator -- edit this
`exercises/calculator-bugs/starter/test-calculator.js`	Test suite -- read only
`exercises/calculator-bugs/starter/.eslintrc.json`	ESLint configuration -- read only
`exercises/calculator-bugs/starter/analysis-report-template.md`	Your report -- fill this out
`exercises/calculator-bugs/starter/package.json`	npm project -- do not edit

Step-by-step

Step 1: Install dependencies

cd modules/module1-foundations/exercises/calculator-bugs/starter
npm install

This creates a node_modules/ directory with ESLint.

Step 2: Run static analysis (ESLint)

npx eslint calculator.js

ESLint examines the source code without executing it and reports issues based on the rules configured in .eslintrc.json. Record every finding (line number, rule name, description) in Part 1 of the analysis report.

The enabled ESLint rules are:

Rule	What it catches
`no-undef`	References to undefined variables
`no-unreachable`	Code after `return` statements
`no-fallthrough`	Missing `break` in `switch` cases
`eqeqeq`	`==` instead of `===` (type coercion risk)
`no-unused-vars`	Declared but never-used variables
`no-constant-condition`	`if (true)` and similar always-true/false guards

Step 3: Run dynamic analysis (test suite)

node test-calculator.js

The test suite runs 16 tests that exercise the calculator functions at runtime. Some tests will PASS; others will FAIL. Record each failure (test name, error message, root cause) in Part 2 of the analysis report.

Step 4: Compare the two approaches

Fill out Parts 3 and 4 of analysis-report-template.md:

Which bugs did only static analysis catch?
Which bugs did only dynamic analysis catch?
Which bugs were found by both approaches?
Why can't either approach catch everything on its own?

Step 5: Fix all 8 bugs

Go back to calculator.js and fix every bug. After fixing, re-run both tools to confirm:

npx eslint calculator.js        # should report 0 errors, 0 warnings
node test-calculator.js          # all tests should PASS

The 8 bugs at a glance

The source comments label each bug (Bug 1 through Bug 8). Do not read these comments until you have tried to find them with the tools first.

Bug #   Function      Category
─────   ──────────    ────────────────────────
  1     add()         Undefined variable
  2     subtract()    Unreachable code
  3     calculate()   Switch fallthrough
  4     divide()      Division by zero
  5     factorial()   Infinite recursion
  6     multiply()    Type coercion (== vs ===)
  7     power()       Unused variable
  8     absolute()    Constant condition

Self-check

When you are done:

ESLint reports no issues
The test suite reports all tests passed
Your analysis report has all four parts filled out with concrete findings

Starter Files

starter

starter/analysis-report-template.md

Read-only

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