IE7中的JavaScript错误& IE8：SCRIPT5007：无法获取属性'newQuestion'的值：object为null或undefined [英] JavaScript error in IE7 & IE8: SCRIPT5007: Unable to get the value of property 'newQuestion': object is null or undefined

问题描述

我一直在寻找并无法提出解决方案。以下代码在IE9，Chrome，FF和Safari中完美运行。但是，当您在IE7或IE8中点击开始时会出现以下错误：

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:

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

有争议的代码在这里：

//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>";
    }   
}

您可以查看演示这里。

我真的认为我已经阅读了所有相关问题，但仍然无法想出解决方案。如果有任何其他信息有用，请告诉我。

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.

更新：

为了澄清，我正在测试在IE9中打开了兼容模式。如果有人确实安装了IE7或IE8，我会知道你的结果。无论如何，代码似乎要执行到这里：

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:

    //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)'>";
    },

点击开始按钮后，我收到错误，因为 this.varName 返回 undefined 。

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

推荐答案

在您的代码中：

> //The quiz object

实际上是一个函数对象，而不是普通对象。您是否希望将其称为构造函数？我无法进入演示。

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.

可能这样：

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

被视为语法错误，因为它以逗号而不是以逗号结尾分号。不，不是。

您的问题在这里：

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

全局变量在IE 8中不可枚举（可能之前），所以你永远找不到你正在寻找的sQuiz实例，并且 this.varName 仍未定义（实际上，该对象将没有 varName 属性所有，除非你在其他地方添加其他方式）。

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.varName remains undefined (actually, the object will not have a varName property at all, unless you add it some other way elsewhere).

你需要使用一些其他方法来引用实例 - 也许使用模块模式并保持一个闭包中的引用，或每个实例的引用数组。

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.

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