Front-end test-2016 Ali front-end Development Engineer Pen Question 6,7,8 problem solution

2016 Ali front-end Development Engineer Pen Test (only questions, no answer):

Http://www.cnblogs.com/sdgf/archive/2015/08/18/4740698.html

Question 6th: Please fill in the answer in ____, so as to achieve the requirements of the topic

var arr = [1, 2, 3, 4, 5];var result = Arr.sort (_______________________________). Join ("+"); Console.log (result);

answer : In sorting, if you need to sort by a certain rule, you can add a custom function:

If from large to small arrange: function (A, b) {return b-a;};

If you are from small to large: function (A, b) {return a-A;};

A more detailed description of the sort method for array:

Https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/toString

Question 7th: Turning a literal object into an instance of a class

function Type () {}var a = {};______________//a instanceof Type = = = True

answer : You need to modify the type of a in this topic, so we need to know: instanceof operator code

function instance_of (L, R) {//l represents the left expression, R represents the right expression  var O = R.prototype;　　The display prototype L = l.__proto__ of R is taken  ; Take the implicit prototype of L  while (true) {     if (L = = = null)       return false;     if (o = = = L)//Here Focus: When O is strictly equal to L, returns true to return True       ;     L = l.__proto__;   }  }
Detailed Description: http://www.ibm.com/developerworks/cn/web/1306_jiangjj_jsinstanceof/

Knowing what's above, we learned that the insanceof decision is based on whether the __proto__ of the instance object is strictly equivalent to the prototype property of the constructor that created the object. That

The instance object. __proto__ = = = constructor. prototype.

So the solution to this problem is to add the __proto__ attribute to a and make it equal to the prototype property of type.

　　　Code Implementation : a.__proto__ = Type.prototype;

Question 8th: Add the following function to determine that p is an array

function IsArray (p) {  return object.prototype._____.apply (p) = = = ' _____ ';  }

Answer: the question needs to be understood: about the use of the Object.prototype.toString () method:

Https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/toString

So the solution to this problem is: toString [object Array]

The above content is purely personal opinion, welcome to correct the mistake, I am also JS beginner.

Front-end test-2016 Ali front-end Development Engineer Pen Question 6,7,8 problem solution