freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/rosetta-code/accumulator-factory.english.md

title	id	challengeType
Accumulator factory	594810f028c0303b75339ace	5

Description

Create a function that takes a single (numeric) argument and returns another function that is an accumulator. The returned accumulator function in turn also takes a single numeric argument, and returns the sum of all the numeric values passed in so far to that accumulator (including the initial value passed when the accumulator was created).

Rules:

Do not use global variables.

Hint:

Closures save outer state.

Instructions

Tests

tests:
  - text: <code>accumulator</code> is a function.
    testString: assert(typeof accumulator === 'function', '<code>accumulator</code> is a function.');
  - text: <code>accumulator(0)</code> should return a function.
    testString: assert(typeof accumulator(0) === 'function', '<code>accumulator(0)</code> should return a function.');
  - text: <code>accumulator(0)(2)</code> should return a number.
    testString: assert(typeof accumulator(0)(2) === 'number', '<code>accumulator(0)(2)</code> should return a number.');
  - text: Passing in the values 3, -4, 1.5, and 5 should return 5.5.
    testString: assert(testFn(5) === 5.5, 'Passing in the values 3, -4, 1.5, and 5 should return 5.5.');

Challenge Seed

function accumulator (sum) {
  // Good luck!
}

After Test

const testFn = typeof accumulator(3) === 'function' && accumulator(3);
if (testFn) {
  testFn(-4);
  testFn(1.5);
}

Solution

function accumulator (sum) {
  return function (n) {
    return sum += n;
  };
}