Deep Flatten Array ใน JavaScript: flat() และ concat.apply()

Flatten Array (ลึกลงไป)

รวม Nested Arrays ทุกระดับให้กลายเป็น 1-D Array

1. Array.flat() (ES2019 - แนะนำ)

<script>
  const arr = [1, 2, [2, 3, [4, 5, [6, 9]]]];
  
  // Depth 2
  console.log(arr.flat(2)); // [1, 2, 2, 3, 4, 5, 6, 9]
  
  // Infinite Depth
  console.log(arr.flat(Infinity)); // [1, 2, 2, 3, 4, 5, 6, 9]
</script>

2. concat.apply() (Legacy)

<script>
  var arrays = [1, 2, [3, 4, [5, 6]], 9];
  var merged = [].concat.apply([], arrays); // 1 Level Only!
  console.log(merged); // [1, 2, 3, 4, [5, 6], 9] - Not Deep!
</script>

Warning: concat.apply Flatten แค่ 1 Level เท่านั้น!

3. Recursive Deep Flatten (Custom)

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

console.log(deepFlatten([1, [2, [3, [4]]]])); // [1, 2, 3, 4]

4. Generator Function (Memory Efficient)

function* flattenGen(arr) {
  for (const item of arr) {
    if (Array.isArray(item)) yield* flattenGen(item);
    else yield item;
  }
}

console.log([...flattenGen([1, [2, [3, [4]]]])]); // [1, 2, 3, 4]

Comparison