1// using recursion, .reduce() and .concat() methods
2// works with arrays of any depth
3
4function flatten(arr)
5{
6	return arr.reduce((acc, cur) => acc.concat(Array.isArray(cur) ? flatten(cur) : cur), []);
7};
8
9const arr = [[1,2],[3,[4,[5]]]];
10
11const flattened = flatten(arr);
12console.log(flattened);
13
14/*
15	Output: [ 1, 2, 3, 4, 5 ]
16*/

1// flat(depth), 
2// depth is optional: how deep a nested array structure 
3//		should be flattened.
4//		default value of depth is 1 
5
6const arr1 = [1, 2, [3, 4]];
7arr1.flat(); 
8// [1, 2, 3, 4]
9
10const arr2 = [1, 2, [3, 4, [5, 6]]];
11arr2.flat();
12// [1, 2, 3, 4, [5, 6]]
13
14const arr3 = [1, 2, [3, 4, [5, 6]]];
15arr3.flat(2);
16// [1, 2, 3, 4, 5, 6]
17
18const arr4 = [1, 2, [3, 4, [5, 6, [7, 8, [9, 10]]]]];
19arr4.flat(Infinity);
20// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

1var arrays = [
2  ["$6"],
3  ["$12"],
4  ["$25"],
5  ["$25"],
6  ["$18"],
7  ["$22"],
8  ["$10"]
9];
10var merged = [].concat.apply([], arrays);
11
12console.log(merged);

1var multiDimensionArray = [["a"],["b","c"],["d"]]; //array of arrays
2var flatArray = Array.prototype.concat.apply([], multiDimensionArray); //flatten array of arrays
3console.log(flatArray); // [ "a","b","c","d"];

1const arr = [1, 2, [3, 4]];
2
3// To flat single level array
4arr.flat();
5// is equivalent to
6arr.reduce((acc, val) => acc.concat(val), []);
7// [1, 2, 3, 4]
8
9// or with decomposition syntax
10const flattened = arr => [].concat(...arr);
11

1var result = [];
2function arrayFlatter (data, result){
3  if (!Array.isArray(data))
4    result.push(data);
5  else if (Array.isArray(data)){
6    let i = 0; 
7    for (i = 0; i < data.length; i++){
8      arrayFlatter (data[i], result);
9    }
10  }
11}
12
13
14arrayFlatter (nestedArr, result)
15