JavaScript对嵌套数组做扁平化处理

  function flatten(arr){
    var result = [];
    if(!arr.length) return [];
    for(var i in arr){
      if(typeof arr[i] === 'object'){
        result = result.concat(flatten(arr[i]));
      }else{
        result.push(arr[i]);
      }
    }
    return result;
  }
  var arr = [1,2,3,[4,5,6]];
  console.log(arr); // [1, 2, 3, Array(3)]
  console.log(flatten(arr)); // [1, 2, 3, 4, 5, 6]