1 if (!Array.prototype.flat) { 2     Array.prototype.flat = function (num = 1) { 3         if (!Number(num) || Number(num) < 0) { 4             return this; 5         } 6         var arr = [] 7         this.forEach((item) => { 8             if (Array.isArray(item)) { 9                 arr = arr.concat(item.flat(--num))10             } else {11                 arr.push(item)12             }13         })14         return arr15     }16 }

测试用例

1 const arr = [1, [2, [3, 'a', [4]]]] 2  3 console.log(arr.flat('dsdsadf'));  // [1, [2, [3, 'a', [4]]]] 4 console.log(arr.flat(-32)); // [1, [2, [3, 'a', [4]]]] 5 console.log(arr.flat(0));   // [1, [2, [3, 'a', [4]]]] 6 console.log(arr.flat('1'));   // [1, 2, [3, 'a', [4]]] 7 console.log(arr.flat('2'));    // [1, 2, 3, 'a', [4]] 8 console.log(arr.flat(3));       // [1, 2, 3, 'a', 4] 9 console.log(arr.flat(Infinity));     // [1, 2, 3, 'a', 4]10 console.log(arr.flat('Infinity'));   // [1, 2, 3, 'a', 4]