Flat array

flat-array.js

let someArray = [[1, 2, [3]], 4];

function flatArray(arrayToFlat) {
	let arrayFlattened = [];
	if (!Array.isArray(arrayToFlat)) {
		return 'This is not an object of type Array';
	}
	function flat(arrayToFlat) {
		arrayToFlat.map((arrayItem, index, arr) => {
			if (Array.isArray(arrayItem)) {
				flat(arrayItem);
			} else {
				arrayFlattened.push(arrayItem);
			}
			;
		});
		return arrayFlattened;
	}

	return flat(arrayToFlat);
}
flatArray(someArray); // [1,2,3,4]



// TESTING
function it(shouldMessage, testCase) {
	return {
		toEqual: (expected) => compareArrays(testCase, expected) ? `"${shouldMessage}" succeded` : `"${shouldMessage}" failed`
	};
}

// This function do not check for equality of literal objects
function compareArrays(testCase, expected) {
	switch (Array.isArray(testCase)) {
		case true:
			return testCase.length === expected.length && testCase.every((element, index) => element === expected[index]);
			break;
		default:
			return testCase === expected;
	}
}

let initialArray = [[1, 2, [3]], 4],
	result = [1, 2, 3, 4];

it('Should flat the array with the correct output', flatArray(initialArray)).toEqual([1, 2, 3, 4]);
it('Should return error message if parameter not Array', flatArray(1)).toEqual("This is not an object of type Array");