An array of arbitrarily nested arrays of integers into a flat array of integers

flatten.js

/*
Deep Flatten a nested array.
Reduce if the child is an array, else concattenate the element to the the parent array.

*/


var deepFlatten = (r, a) => Array.isArray(a) ? a.reduce(deepFlatten, r) : r.concat(a)


function test_flatten(){
var arr1 = [[1,2,[3]],4];
var arr2 = [1,[2,[3,[4],5,],6],7];


var outputArray_1 = arr1.reduce(deepFlatten, []);
var outputArray_2 = arr2.reduce(deepFlatten, []);

console.log('Flattened array 1:', outputArray_1);
console.log('Flattened array 2:', outputArray_2);

}

test_flatten();