five_num.js

// 拿到嵌套数组的前五个
(function(){
  var first_arr = [[1,3,4], [3,4,5,6,0], [34,56,23,56,34] [32,45]];// => [[1,3,4],[3,4]]
  var second_arr = [[1,3,4,7], [3,4,5,6,0], [34,56,23,56,34] [32,45]]; // => [[1,3,4,7],[3]]
  var third_arr = [[1,3,4,7,9], [3,4,5,6,0], [34,56,23,56,34] [32,45]]; // => [[1,3,4,7,9]]
  var fourth_arr = [[1,3,4,7,9, 10], [3,4,5,6,0], [34,56,23,56,34] [32,45]]; // => [[1,3,4,7,9]]

  function five(arr) {
    var count = 0, result = [], left_count = 0;
    for (var i = 0; i <= arr.length; i++) {
      left_count = 5 - count;
      if(count < 5 && arr[i].length <= left_count) {
        result.push(arr[i]);
        count += arr[i].length;
      } else if (count < 5 && arr[i].length > left_count) {
        result.push(arr[i].slice(0, left_count));
        break;
      } else {
        break;
      }
    };
    return result;
  }

  console.log( five(first_arr) );
  console.log( five(second_arr) );
  console.log( five(third_arr) );
  console.log( five(fourth_arr) );
})();