Array.prototype.flat()

flat() 函數以遞迴方式將特定深度的子陣列重新串接成為一新的陣列

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語法

var newArray = arr.flat([depth]);

參數

depth 選擇性

指定巢狀陣列展開的深度。預設為1。

回傳值

函數將會回傳一個由原先陣列的子陣列串接而成的新陣列。

範例

展開巢狀陣列

var arr1 = [1, 2, [3, 4]];
arr1.flat(); 
// [1, 2, 3, 4]

var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat();
// [1, 2, 3, 4, [5, 6]]

var arr3 = [1, 2, [3, 4, [5, 6]]];
arr3.flat(2);
// [1, 2, 3, 4, 5, 6]

當遭遇空元素時

flat()函數會自動清除陣列中空的元素

var arr4 = [1, 2, , 4, 5];
arr4.flat();
// [1, 2, 4, 5]

替代方案

reduce 與 concat

var arr1 = [1, 2, [3, 4]];
arr1.flat();

//展開單層陣列
arr1.reduce((acc, val) => acc.concat(val), []);// [1, 2, 3, 4]

//欲展開更深層的巢狀結構請使用reduce與concat的遞迴
function flattenDeep(arr1) {
   return arr1.reduce((acc, val) => Array.isArray(val) ? acc.concat(flattenDeep(val)) : acc.concat(val), []);
}
flattenDeep(arr1);// [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]

//使用stack來實作非遞迴的展開
var arr1 = [1,2,3,[1,2,3,4, [2,3,4]]];
function flatten(input) {
  const stack = [...input];
  const res = [];
  while (stack.length) {
    // pop value from stack
    const next = stack.pop();
    if (Array.isArray(next)) {
      // push back array items, won't modify the original input
      stack.push(...next);
    } else {
      res.push(next);
    }
  }
  //reverse to restore input order
  return res.reverse();
}
flatten(arr1);// [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]

// 递归版本的反嵌套
function flatten(array) {
  var flattend = [];
  (function flat(array) {
    array.forEach(function(el) {
      if (Array.isArray(el)) flat(el);
      else flattend.push(el);
    });
  })(array);
  return flattend;
}

規範

瀏覽器相容性

See also

• Array.prototype.flatMap()
• Array.prototype.map()
• Array.prototype.reduce()
• Array.prototype.concat()