JavaScript 扁平化多維陣列

const a = ['1',['2','3'],['4','5'],['6','7']];

const b = ['1', '2', '3', '4', '5', '6', '7'];

const a = ['1',['2','3'],['4','5',['6','7']]];
const a = ['1',['2','3'],['4','5'],['6','7']];
const newArray = [].concat.apply([], a);

const a = ['1',['2','3'],['4','5'],['6','7']];

const newArray = a.reduce((a, b) => {
  return a.concat(b);
})

const a = [['2','3'],['4','5'],['6','7']];

const newArray = a.reduce((a, b) => {
  return a.concat(b);
})

const a = ['1',['2','3'],['4','5'],['6','7']];

const array = [];
const newArray = a.forEach((item, index) => {
  item.forEach((b) => {
    array.push(b);
  })
})

const a = [['2','3'],['4','5'],['6','7']];

const array = [];
const newArray = a.forEach((item, index) => {
  item.forEach((b) => {
    array.push(b);
  })
})

const a = ['1',['2','3'],['4','5'],['6','7']];

const newArray = [].concat(...a);

const a = ['1',['2','3'],['4','5'],['6','7']];

const newArray = a.flat(Infinity);

// 練習二：壓平陣列
// 請寫出一個 function flatten，接收一個多維陣列並回傳「壓平」後的陣列。
// flatten([1, 2, 3]) 預期回傳值：[1, 2, 3]
// flatten([1, 2, [1, 2], [1, 3], 6]) 預期回傳值：[1, 2, 1, 2, 1, 3, 6]
// flatten([1, [2, [3, [4]], 5], 6]) 預期回傳值：[1, 2, 3, 4, 5, 6]
// 遞迴
function flatten(array) {
  let tempArray = [];
  for (let i = 0; i < array.length; i++) {
    if (Array.isArray(array[i])) {
      // 壓平陣列 CALL 自己
      let flat = flatten(array[i]); // ex [1, 2, 3]
      // 推入陣列
      for (let j = 0; j < flat.length; j++) {
        tempArray.push(flat[j]);
      }
    } else {
      tempArray.push(array[i]);
    }
  }
  return tempArray;
}