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

title, id, challengeType

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

console.info('after the test');

Solution

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