手写flat函数

扩展运算符 + 递归

无指定层数：扁平化数组

function flat(arr) {
  let result = [];
  arr.forEach(item => {
    if (Array.isArray(item)) {
      result = result.concat(arguments.callee(item));
    } else {
      result.push(item);
    }
  });
  return result;
}
console.log(flat(arr))

let arr = [1,[3,4,[45]]];

function flat(arr) {
  let result = [];
  arr.forEach(item => {
    if (Array.isArray(item)) {
      result.push(...arguments.callee(item));
    } else {
      result.push(item);
    }
  });
  return result;
}
console.log(flat(arr));

reduce

reduce实现flat

let arr = [24,6,[12,[4]]]
function flat(arr,num=1){
  return num > 0 
    ? arr.reduce((pre, cur) =>        
     pre.concat(Array.isArray(cur)? flat(cur,num-1) : cur),[])
     :arr.slice();
}
console.log(flat(arr,1))