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 flattenArray = function(data) {
2	return data.reduce(function iter(r, a) {
3		if (a === null) {
4			return r;
5		}
6		if (Array.isArray(a)) {
7			return a.reduce(iter, r);
8		}
9		if (typeof a === 'object') {
10			return Object.keys(a).map(k => a[k]).reduce(iter, r);
11		}
12		return r.concat(a);
13	}, []);
14}
15console.log(flattenArray(data))
16
17//replace data with your array
18

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);

1// Although this now may be an older version of how to faltten an 
2// array of arrays. I still want to post it so some may have an understanding 
3// of how it works
4
5function falltenArray(arr) {
6  
7  let result = [...arr];
8  let flattened = false;
9  let counter = 0;
10  
11  while (flattened === false){
12	// checks to see if the element at the counter index is an array
13      if (Array.isArray(result[counter])){
14        // unpacks the current array element back into the array
15        result.splice(counter, 1, ...result[counter]);
16        // if so the counter should start at the beginning of the array
17        counter = 0;
18        
19      } else {
20        counter += 1;
21      }
22
23      if (counter === result.length){
24        flattened = true;
25      }
26  }
27  
28  return result;
29}

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

1function flatten(arr) {
2  const result = []
3
4  arr.forEach((i) => {
5    if (Array.isArray(i)) {
6      result.push(...flatten(i))
7    } else {
8      result.push(i)
9    }
10  })
11  
12  return result
13}
14
15// Usage
16const nested = [1, 2, 3, [4, 5, [6, 7], 8, 9]]
17
18flatten(nested) // [1, 2, 3, 4, 5, 6, 7, 8, 9]