Question

我正在为SkillCrush开发一个项目，并且遇到“未定义”错误，感觉好像我已在代码顶部定义了变量。我100％知道我做错了事，但不确定是什么。有什么建议吗？

var createPolitician = function (name)
{
    var politician = {}; //is this not defined here?
    politician.name = name;
    politician.electionResults = null;
    politician.totalVotes = 0;

    return politician;
};

var oscar = createPolitician("Oscar Jiminez");
var luke = createPolitician("Luke Spencer");

oscar.electionResults = [5, 1, 7, 2, 33, 6, 4, 2, 1, 14, 8, 3, 1, 11, 11, 0, 5, 3, 3, 3, 7, 4, 8, 9, 3, 7, 2, 2, 4, 2, 8, 3, 15, 15, 2, 12, 0, 4, 13, 1, 3, 2, 8, 21, 3, 2, 11, 1, 3, 7, 2];

luke.electionResults = [4, 2, 4, 4, 22, 3, 3, 1, 2, 15, 8, 1, 3, 9, 0, 6, 1, 5, 5, 1, 3, 7, 8, 1, 3, 3, 1, 3, 2, 2, 6, 2, 14, 0, 1, 6, 7, 3, 7, 3, 6, 1, 3, 17, 3, 1, 2, 11, 2, 3, 1];

oscar.electionResults[9] = 1;
luke.electionResults[9] = 28;

oscar.electionResults[4] = 17;
luke.electionResults[4] = 38;

oscar.electionResults[43] = 11;
luke.electionResults[43] = 27;

console.log(oscar.electionResults);
console.log(luke.electionResults);

politician.countTotalVotes = function() 
{
    this.totalVotes = 0;

    for (var i = 0; i < this.electionResults.length; i++);
    {
        this.totalVotes = this.totalVotes + this.electionResults[i];
    }
}

oscar.countTotalVotes();
luke.countTotalVotes();

console.log(oscar.totalVotes);
console.log(luke.totalVotes);

错误：

"error"
    "ReferenceError: politician is not defined
    at reloyur.js:32:1"

Answer 1

将countTotalVotes函数移至创建函数：

var createPolitician = function (name)
{

  var politician = {}; 
  politician.name = name;
  // set to an empty array so this is defined
  politician.electionResults = []; 
  politician.totalVotes = 0;
  // here politician exists, add a function to the object that you can call later
  politician.countTotalVotes = function() 
  {
     this.totalVotes = 0;
     for (var i = 0; i < this.electionResults.length; i++)
     {
        this.totalVotes = this.totalVotes + this.electionResults[i];
      }
  }

  return politician;

};

Answer 2

 politician.countTotalVotes = ...

这不会起作用，因为politician仅在创建luke或oscar时存在（然后指向其中之一）。相反，您可以这样做：

luke.countTotalVotes = oscar.countTotalVotes = function() { /*...* };

但是对于更多的政治家来说，情况变得有些复杂。但是，您可以将政治家传递给以下人员：

function countTotalVotes(politician) {
  //...
}

countTotalVotes(luke);

或者您使用继承的力量。

Answer 3

正如我在评论中建议的那样，您可以将Politician重写为class，这基本上为您提供了可重用功能的模板。如果您不熟悉此概念，则一般来说，"prototypal inheritance"是跟进该主题的好词。现在，这是使用class重写脚本的方法：

class Politician {
  constructor (name) {
    this.name = name;
    this.electionResults = [];
  }

  // no need to even write a .countTotalVotes() method
  // just define .totalVotes as a getter that does the work
  get totalVotes () {
    var total = 0;

    for (var i = 0; i < this.electionResults.length; i++) {
      total += this.electionResults[i];
    }

    return total;
  }
}

var oscar = new Politician("Oscar Jiminez");
var luke = new Politician("Luke Spencer");

oscar.electionResults = [5, 1, 7, 2, 33, 6, 4, 2, 1, 14, 8, 3, 1, 11, 11, 0, 5, 3, 3, 3, 7, 4, 8, 9, 3, 7, 2, 2, 4, 2, 8, 3, 15, 15, 2, 12, 0, 4, 13, 1, 3, 2, 8, 21, 3, 2, 11, 1, 3, 7, 2];

luke.electionResults = [4, 2, 4, 4, 22, 3, 3, 1, 2, 15, 8, 1, 3, 9, 0, 6, 1, 5, 5, 1, 3, 7, 8, 1, 3, 3, 1, 3, 2, 2, 6, 2, 14, 0, 1, 6, 7, 3, 7, 3, 6, 1, 3, 17, 3, 1, 2, 11, 2, 3, 1];

oscar.electionResults[9] = 1;
luke.electionResults[9] = 28;

oscar.electionResults[4] = 17;
luke.electionResults[4] = 38;

oscar.electionResults[43] = 11;
luke.electionResults[43] = 27;

// console.log(oscar.electionResults);
// console.log(luke.electionResults);

// these are no longer required
// oscar.countTotalVotes();
// luke.countTotalVotes();

console.log(oscar.name, 'has', oscar.totalVotes, 'votes');
console.log(luke.name, 'has', luke.totalVotes, 'votes');

Answer 4

错误消息应随附行号和列号。在这种情况下，错误发生在第32行：

politician.countTotalVotes = function()

在createPolitician函数的定义中，您声明了一个名为politician的变量。 var创建一个变量，该变量驻留在声明该函数的函数中。如果它不在函数内部，则创建一个全局变量。

您保留了在其中声明变量的函数，因此该函数不再可用。

如果考虑一下，以后再使用该politician变量将非常模棱两可。它指的是什么？

如果您希望能够致电给政治人物countTotalVotes()，那么帕特里克（Patrick）有关使用班级的评论是一个不错的选择。您还可以将函数分配给从politician返回的createPolitician对象-这将为政客的每个实例提供其自己的函数副本。

Answer 5

我更正了您在代码中的错误。您可以像下面这样更改代码：

function createPolitician(name)
{
    var politician = 
    {
        name: name,
        electionResults: null,
        totalVotes: 0,

        countTotalVotes: function() 
        {
            //this.totalVotes = 0; <- irrelevant because you use it only one time
            for(var i = 0; i < this.electionResults.length; i++)//";" symbol  on the end is your mistake too
            {
                this.totalVotes += this.electionResults[i];
            }

        }
    };
    return politician;
};

var oscar = createPolitician("Oscar Jiminez");
var luke = createPolitician("Luke Spencer");

oscar.electionResults = [5, 1, 7, 2, 33, 6, 4, 2, 1, 14, 8, 3, 1, 11, 11, 0, 5, 3, 3, 3, 7, 4, 8, 9, 3, 7, 2, 2, 4, 2, 8, 3, 15, 15, 2, 12, 0, 4, 13, 1, 3, 2, 8, 21, 3, 2, 11, 1, 3, 7, 2];

luke.electionResults = [4, 2, 4, 4, 22, 3, 3, 1, 2, 15, 8, 1, 3, 9, 0, 6, 1, 5, 5, 1, 3, 7, 8, 1, 3, 3, 1, 3, 2, 2, 6, 2, 14, 0, 1, 6, 7, 3, 7, 3, 6, 1, 3, 17, 3, 1, 2, 11, 2, 3, 1];

oscar.electionResults[9] = 1;
luke.electionResults[9] = 28;

oscar.electionResults[4] = 17;
luke.electionResults[4] = 38;

oscar.electionResults[43] = 11;
luke.electionResults[43] = 27;

console.log(oscar.electionResults);
console.log(luke.electionResults);

oscar.countTotalVotes();
luke.countTotalVotes();

console.log(oscar.name, 'has', oscar.totalVotes, 'votes');
console.log(luke.name, 'has', luke.totalVotes, 'votes');

Answer 6

这与variable scope有关。 在createPolitician函数之外声明政治家对象变量 ，以便您访问该函数。无法访问其范围，这就是为什么您会得到未定义的错误的原因。

我认为我的JavaScript代码已定义时，出现“未定义”错误

6 个答案: