Flatten an array

flatten-array.js

function flatten(arr) {
	if (!Array.isArray(arr)) throw new Error('flatten takes an array as a parameter');
    return arr.reduce(function(newArr, el) {
        if (Array.isArray(el)) return flatten(newArr.concat(el));
        return newArr.concat(el);
    }, []);
}

//uses jasmine as a testing framework
describe('Flattening an array', function() {
	it('should flatten nested array of integers to an array of integers', function() {
		var arr = [1, 2, [3, 4], [[[5], [6, 7], 8], [9, [[10, 11, [12, 13]]]]], 14];
		expect(flatten(arr)).toEqual([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]);
	});
	
	it('should flatten nested array of generic types to an array of generic types', function() {
		var arr = [1, 2, [3, 4], [[[5], [6, 7], 8], [9, [[{name: 'hello'}, 'foo', [12, 13]]]]], 14];
		expect(flatten(arr)).toEqual([1, 2, [3, 4], [[[5], [6, 7], 8], [9, [[{name: 'hello'}, 'foo', [12, 13]]]]], 14]);
	});
	
	it('should return empty array', function() {
		expect(flatten([])).toEqual([]);
	});
	
	it('should throw an error', function() {
		expect(function() { flatten({}); }).toThrow(new Error('flatten takes an array as a parameter'));
	});
});