let arr = [1, [2, 3, [4, 5, [6, 7], [8, 9, 10, 11, 12]]]];

function flattenList(nestedArr) {
  let newFlattenList = [];

  const handleFlat = (array) => {
    let count = 0;
    while (count < array.length) {
      let item = array[count];
      if (Array.isArray(item)) {
        handleFlat(item);
      } else {
        newFlattenList.push(item);
      }
      count++;
    }
  };
  handleFlat(nestedArr);
  return newFlattenList;
}`enter code here`

console.log(flattenList(arr));

CodeSandBox链接

这是递归方法。。。

function flatten(arr){
    let newArray = [];
    for(let i=0; i< arr.length; i++){
        if(Array.isArray(arr[i])){
          newArray =  newArray.concat(flatten(arr[i]))
        }else{
          newArray.push(arr[i])
        }
    }
  return newArray; 
}

console.log(flatten([1, 2, 3, [4, 5] ])); // [1, 2, 3, 4, 5]
console.log(flatten([[[[1], [[[2]]], [[[[[[[3]]]]]]]]]]))  // [1,2,3]
console.log(flatten([[1],[2],[3]])) // [1,2,3]

我提出了两个没有递归的简短解决方案。从计算复杂性的角度来看，它们不是最优的，但在一般情况下工作良好：

let a = [1, [2, 3], [[4], 5, 6], 7, 8, [9, [[10]]]];

// Solution #1
while (a.find(x => Array.isArray(x)))
    a = a.reduce((x, y) => x.concat(y), []);

// Solution #2
let i = a.findIndex(x => Array.isArray(x));
while (i > -1)
{
    a.splice(i, 1, ...a[i]);
    i = a.findIndex(x => Array.isArray(x));
}

[1,[2,3],[4,[5,6]]].reduce(function(p, c) {
    return p.concat(c instanceof Array ? 
                    c.reduce(arguments.callee, []) : 
                    [c]); 
}, []);

这里有一个简短的函数，它使用一些较新的JavaScript数组方法来展平n维数组。

function flatten(arr) {
  return arr.reduce(function (flat, toFlatten) {
    return flat.concat(Array.isArray(toFlatten) ? flatten(toFlatten) : toFlatten);
  }, []);
}

用法：

flatten([[1, 2, 3], [4, 5]]); // [1, 2, 3, 4, 5]
flatten([[[1, [1.1]], 2, 3], [4, 5]]); // [1, 1.1, 2, 3, 4, 5]

以下代码将压平深度嵌套的数组：

/**
 * [Function to flatten deeply nested array]
 * @param  {[type]} arr          [The array to be flattened]
 * @param  {[type]} flattenedArr [The flattened array]
 * @return {[type]}              [The flattened array]
 */
function flattenDeepArray(arr, flattenedArr) {
  let length = arr.length;

  for(let i = 0; i < length; i++) {
    if(Array.isArray(arr[i])) {
      flattenDeepArray(arr[i], flattenedArr);
    } else {
      flattenedArr.push(arr[i]);
    }
  }

  return flattenedArr;
}

let arr = [1, 2, [3, 4, 5], [6, 7]];

console.log(arr, '=>', flattenDeepArray(arr, [])); // [ 1, 2, [ 3, 4, 5 ], [ 6, 7 ] ] '=>' [ 1, 2, 3, 4, 5, 6, 7 ]

arr = [1, 2, [3, 4], [5, 6, [7, 8, [9, 10]]]];

console.log(arr, '=>', flattenDeepArray(arr, [])); // [ 1, 2, [ 3, 4 ], [ 5, 6, [ 7, 8, [Object] ] ] ] '=>' [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]