IE7 和 IE8 中的 JavaScript 错误：SCRIPT5007：无法获取属性“newQuestion”的值：对象为空或未定义

JavaScript error in IE7 & IE8: SCRIPT5007: Unable to get the value of property 'newQuestion': object is null or undefined

提问by ARP

I've been looking all over and can't come up with a solution. The following code works perfectly in IE9, Chrome, FF, and Safari. However, when you hit "Start" in IE7 or IE8 you get the following error:

我一直在寻找，但无法提出解决方案。以下代码在 IE9、Chrome、FF 和 Safari 中完美运行。但是，当您在 IE7 或 IE8 中点击“开始”时，您会收到以下错误：

SCRIPT5007: Unable to get the value of property 'newQuestion': object is null or undefined

The code at issue is here:

有问题的代码在这里：

//This is used to reduce some code size and not type document.getElementById(a) each time
function DOMelem(a) {
    return document.getElementById(a);
}
//This is used to round numbers
function roundTo(a,b) {
    a=a*Math.pow(10,b);
    a=Math.round(a);
    a=a/Math.pow(10,b);
    return a;
}
//The quiz object
function sQuiz(a,c,init) {
    //This part is used to get the variable used by the user
    this.getName=function() {
        for(var v in window) {
            if(window[v] instanceof sQuiz) {
                this.varName=v;
            }
        }   
    },
    //This will create the first page of the quiz
    this.createQuiz=function() {
        this.getName();
        DOMelem(a).innerHTML="<h1>"+init.intro.qTitle+"</h1>";
        DOMelem(a).innerHTML+="<h2>"+init.intro.qAuthor+"</h2>";
        DOMelem(a).innerHTML+="<h3>"+init.intro.qComments+"</h3><br /><br />";
        DOMelem(a).innerHTML+="<input type='button' value='Start' onClick='"+this.varName+".newQuestion(0)'>";
    },
    //This one will create a random id for the quiz and create a bar for it
    this.createBar=function() {
        id="12391023103091"+Math.round(Math.random()*12391023103091);
        id=id.substr(id.length-14,14);
        this.randBarId=id;
        DOMelem(c).innerHTML="<div class='progress_full' id='pro_"+id+"'><div class='progress_bar' style='width:0%;' id='bar_"+id+"'></div></div>";
    },
    //In this section we check to see if there's a bar, if we must show the results or just show the interface.
    this.newQuestion=function(index) {
        //Create the bar if it does not exist
        if(!DOMelem("pro_"+this.randBarId)||!DOMelem("bar_"+this.randBarId)) {
            eval(this.varName+".createBar()");
        }
        //Show the results page
        if(index>=init.questions.length) {
            eval(this.varName+".showResults()");
        }
        //Show the question interface
        else {
            DOMelem(a).innerHTML="<h1>"+init.questions[index].question+"</h1>";
            for (var i=0;i<init.questions[index].answers.length;i++) {
                DOMelem(a).innerHTML+="<input type='button' name='"+index+"_"+i+"' value='"+init.questions[index].answers[i]+"' onClick='"+this.varName+".checkAnswer("+index+","+i+")'>";
            }
            DOMelem(a).innerHTML+="<input type='submit' id='btn_"+this.randBarId+"' value='Next Question' onClick='"+this.varName+".changeQuestion("+index+")' disabled>";
            DOMelem("bar_"+this.randBarId).style.width=(((index+1)/init.questions.length)*100)+"%";
        }
    },
    //This is used when the user clicks to change the question 
    this.changeQuestion=function(index) {
        return this.newQuestion(index+1);
    },
    //This part handles when the user clicks on an answer, color it, un-disable the button and record the guess
    this.checkAnswer=function(index,i) {
        init.questions[index].guessed=i;
        var inputs=document.getElementById(a).getElementsByTagName("input");
        for(var j=0;j<inputs.length;j++) {
            document.getElementById(a).getElementsByTagName("input")[j].className="";
            if(inputs[i].name==index+"_"+i) {
                document.getElementById(a).getElementsByTagName("input")[i].className="selected";
            }
        }
        DOMelem("btn_"+this.randBarId).disabled=false;
    },
    //This one here shows the result of the quiz.
    this.showResults=function() {
        DOMelem(a).innerHTML="<h1>Results of "+init.intro.qTitle+"</h1>";
        var count=0;
        for(var i=0;i<init.questions.length;i++) {
            if(init.questions[i].guessed==(init.questions[i].correctAnswer-1)) {
                count++;
                DOMelem(a).innerHTML+="<div id='answer' class='correct'>&radic; Question "+(i+1)+"</div>";
            }
            else {
                DOMelem(a).innerHTML+="<div id='answer' class='wrong'>&times; Question "+(i+1)+"</div>";
            }
        }
        var result=roundTo((count/init.questions.length)*100,2);
        DOMelem(a).innerHTML+="<h3 style='clear:both'><br />"+result+"% correct answers.</h3>";
        var tweet=init.tweetText.replace(/--score--/gi,result+"%");
        tweet=tweet.replace(/ /gi,'+');
        tweet="https://www.twitter.com/share?text="+tweet;
        DOMelem(a).innerHTML+="<a href='"+tweet+"'>Tweet it</a>";
    }   
}

You can view a demo here.

您可以在此处查看演示。

I really think I've read about every related question, but still can't come up with a solution. Please let me know if any additional information would be helpful.

我真的认为我已经阅读了所有相关问题，但仍然无法提出解决方案。如果有任何其他信息会有所帮助，请告诉我。

UPDATE:

更新：

To clarify, I am testing in IE9 with compatibility mode turned on. If anyone actually has IE7 or IE8 installed, I would live to know your results. Anyway, the code seems to execute up until here:

澄清一下，我正在 IE9 中测试并打开兼容模式。如果有人真的安装了 IE7 或 IE8，我很想知道你的结果。无论如何，代码似乎一直执行到这里：

    //This will create the first page of the quiz
    this.createQuiz=function() {
        this.getName();
        DOMelem(a).innerHTML="<h1>"+init.intro.qTitle+"</h1>";
        DOMelem(a).innerHTML+="<h2>"+init.intro.qAuthor+"</h2>";
        DOMelem(a).innerHTML+="<h3>"+init.intro.qComments+"</h3><br /><br />";
        DOMelem(a).innerHTML+="<input type='button' value='Start' onClick='"+this.varName+".newQuestion(0)'>";
    },

Once the start button is clicked, I get an error because this.varNamereturns as undefined.

单击开始按钮后，我收到一个错误，因为this.varName返回为undefined.

回答by RobG

In your code:

在您的代码中：

> //The quiz object

Is really a function object, not a plain object. And do you expect to call it as a constructor? I can't get to the demo.

真的是一个函数对象，而不是一个普通的对象。您是否希望将其称为构造函数？我无法进入演示。

Likely this:

大概是这样：

> this.getName=function() {
>     for(var v in window) {
>         if(window[v] instanceof sQuiz) {
>             this.varName=v;
>         }
>     }
> },

is treated as a syntax error because it is terminated with a comma instead of a semi–colon. No, it's not.

被视为语法错误，因为它以逗号而不是分号结尾。不，这不对。

Edit

编辑

Your problem is here:

你的问题在这里：

    for(var v in window) {
         if(window[v] instanceof sQuiz) {
             this.varName=v;
         }
    }

Global variables are not enumerable in IE 8 (and probably earlier), so you never find the instance(s) of sQuiz you are looking for and this.varNameremains undefined (actually, the object will not have a varNameproperty at all, unless you add it some other way elsewhere).

全局变量在 IE 8（可能更早版本）中是不可枚举的，所以你永远找不到你正在寻找的 sQuiz 的实例并且this.varName保持未定义（实际上，对象根本没有varName属性，除非您在其他地方以其他方式添加它）。

You need to use some other method of referencing the instance(s)— perhaps using the module pattern and keeping a reference in a closure, or an array of references to each instance.

您需要使用其他一些方法来引用实例——可能使用模块模式并在闭包中保留一个引用，或者每个实例的引用数组。

回答by tinyd

I'm not 100% sure, but I get a JavaScript error when I load the page in IE. This line:-

我不是 100% 确定，但是当我在 IE 中加载页面时出现 JavaScript 错误。这一行：-

if(window[v] instanceof sQuiz)

is failing - you should check window[v] for null first before instanceof

失败 - 您应该在 instanceof 之前先检查 window[v] 是否为 null