A small tool/exercise for flattening arrays

README.md

For this code exercise I went with a simple recursive solution to drill down into each array element, compiling a master array of the individual elements, aiming for elegant code which is readable and functional and ready to ship as it has tests and was written in a TDD manner (as I try to do for all of my tests).

The tests give you examples of how you would run this tool/code for it's desired effect.

E.g.

const ArrayFlattenerTool = require('./array-flattener.js');
const flatArray = ArrayFlattenerTool([1, [1, [2, [3, 4]]], 5]);

console.log(`My new fancy flat array is: ${flatArray});

return flatArray;

array-flattener-spec.js

const ArrayFlattenerTool = require('./array-flattener-tool.js');

describe('Array flattening tool', () => {
    describe('When passed an array with nested arrays', () => {
        it('Should throw an error when an array is not passed as a parameter', () => {
            try {
                const flatArray = ArrayFlattenerTool();
            } catch (expectedError) {
                expect(expectedError.message).toEqual('Please ensure you pass a valid array to the tool.');
            }
        })

        it('Should return a flattened version of the array', () => {
            const flatArray = ArrayFlattenerTool([1, [1, 2], 3]);
            expect(flatArray).toEqual([1, 1, 2, 3]);
        });

        it('Should flatten a doubly nested array', () => {
            const flatArray = ArrayFlattenerTool([1, [1, [2, 3]], 4]);
            expect(flatArray).toEqual([1, 1, 2, 3, 4]);
        })

        it('Should flatten a triple nested array!', () => {
            const flatArray = ArrayFlattenerTool([1, [1, [2, [3, 4]]], 5]);
            expect(flatArray).toEqual([1, 1, 2, 3, 4, 5]);
        })
    })
});

array-flattener.js

const flattenArray = (arrayToFlatten, newFlatArray) => {
    if (arrayToFlatten.toString().length == 1) {
        newFlatArray.push(arrayToFlatten);
    } else {
        arrayToFlatten.forEach(arrayElement => {
            flattenArray(arrayElement, newFlatArray);
        });
    }
}

module.exports = arrayToFlatten => {

    if (!arrayToFlatten) {
        throw new Error('Please ensure you pass a valid array to the tool.');
    }

    const flatArray = [];
    flattenArray(arrayToFlatten, flatArray);

    return flatArray;
}