JavaScriptintermediate

CODING EXERCISE

Group transactions

Group transactions by category and calculate an exact total for every category.

Requirements

Return the expected value for every provided input.
Keep the solution readable and cover edge cases.
Avoid mutating the input unless the prompt requires it.

Example

Input

[
  {
    "amount": 12,
    "category": "books"
  },
  {
    "amount": 8,
    "category": "books"
  }
]

Expected output

{
  "books": 20
}

Show a hint

Start with the simplest correct solution, then test an empty or minimal input.

tests

RUNTIME OUTPUT

Ready to run the file open above against 1 test.

Runs the open file in a restricted browser worker

A PRACTICAL PLAN

Work through Group transactions with intent.

Translate the contract.Turn the requirements into a short checklist before editing your-solution.js.
Use the example as evidence.Predict the result for the supplied input, then add one boundary case such as an empty value, a limit, or unexpected input.
Review the implementation.Compare your choices against solution.js only after a real attempt.

EXERCISE FAQ

Before you move on.

What does “Group transactions” teach?

This intermediate JavaScript exercise focuses on JavaScript. Its requirements define the exact behavior to implement before you write code.

How should I validate this JavaScript solution?

Start with the displayed example input and expected output, then test a boundary case suggested by the requirements. Open your-solution.js and select Run code. The browser executes that file in an isolated worker against the visible test cases.

When should I open the reference solution?

Attempt Group transactions first. Then open the read-only solution file to compare the contract, edge-case handling, and implementation choices—not simply to copy the final code.

Group transactions

Requirements

Example

Work through Group transactions with intent.

Before you move on.

Related JavaScript exercises.

Build a safe query string

Calculate a cart total in cents

Merge two sorted result lists