flatten array in javascript without flat code example

Example 1: js convert array of arrays to array

// Converts array with multiple values into a single array with all items:
var merged = [].concat.apply([], arrays);

Example 2: how to flatten nested arrays javascript

// using recursion, .reduce() and .concat() methods
// works with arrays of any depth

function flatten(arr)
{
	return arr.reduce((acc, cur) => acc.concat(Array.isArray(cur) ? flatten(cur) : cur), []);
};

const arr = [[1,2],[3,[4,[5]]]];

const flattened = flatten(arr);
console.log(flattened);

/*
	Output: [ 1, 2, 3, 4, 5 ]
*/