javascript - JQuery:选中/取消选中单选按钮

Question

我试图找出脚本中的错误，并希望有人能够告诉我哪里出了问题。这是尝试创建一个基于 JS/Jquery 的测验(javascriptissexy 练习)。

到目前为止，它工作正常，除了:我想使用一个后退按钮来记忆用户之前给出的答案并相应地设置单选按钮。该脚本不会返回，即使我单击前进，它也不会给出任何错误，这可以帮助我查明问题。

再次，我真的很抱歉我无法进一步缩小范围，因为我真的不知道哪些部分相关/不相关。如果有人有一些建议，如何以更好的方式呈现这些“我快要放弃了，因为我不知道如何查明问题”，我会很乐意这样做。

HTML 单选按钮的结构如下:

 <input type="radio" name="radio" id="Option0" value="Option0" />
 <label for ="Option0">Option0</label>

JS/Jquery:

 $(document).ready(function () {
 var allQuestions = [
    {question: "Who is Prime Minister of the United Kingdom?",
        choices: ["David Cameron", "Gordon Brown", "Winston Churchill", "Tony Blair"],
        correctAnswer: 0},
    {question: "Which color has the sky?",
        choices: ["Grey", "Black", "Blue", "Green"],
        correctAnswer: 2},
    {question: "What's on the chain?",
        choices: ["Monster", "Magician", "Bull", "Skull"],
        correctAnswer: 3}
];

var counter = 0;     // Question No currently processed
var points = 0;        // Total points currently reached by the player
var answers = new Array(); // Array of the choices the player made  eg Q1:0

// Back button in a function
function back() {
    if (counter > 0)          //Checks if there is at least one question already answered
    {
        //Goes back one question

        $("#back").show().on('click', function () {
            counter = counter--;
            quiz();
        });      //Executes quiz loading

    }
    else {
        $("#back").hide();         //If there is no previous question existing the back button is deactivated
    }
}


function qload(counter) {
    $("title").text("Question No ");
    $("#question").text(allQuestions[counter].question);
    back();
    for (var i = 0; i < allQuestions[counter].choices.length; i++) {
        $('label[for=Option' + i + ']').html(allQuestions[counter].choices[i]);

        if (answers["Q" + i]) {
            $("#Option" + i).attr("checked","checked");
        }

        else {
            $("#Option" + i).removeAttr('checked');
        }
    }
};
//this is the result screen giving the final amount of points
function result() {
    $("title").text("Your Results");
    for (var i = 0; i < allQuestions.length; i++) {
        if (allQuestions[i].correctAnswer == answers["Q" + i]) {
            points++;
        }


        $("#result").show().text("CONGRATULATIONS! You answered " + points + " out of " + allQuestions.length + " correct!");
        $(".qbox").hide();
        console.log(answers);

    }
}

function welcome() {
    // this is the welcome screen inviting to start the quizz
    $("title").text("Welcome to the JQuery QuizY");
    $(".qbox").hide();
    $("#result").append().html("Random");
    $("#result").append().html("<p id='start'>Start</p>");
    $("#start").on('click', function () {
        quiz();
    });
}

function quiz() {
    $("#start, #result").hide();
    $(".qbox").show();
    qload(counter);
    $("#next").on('click', function () {
        // this checks that one question is selected before processing
        if ($('#Option0').is(':checked')) {
            answers["Q" + counter] = 0;
            counter++;
        }

        else if ($('#Option1').is(':checked')) {
            answers["Q" + counter] = 1;
            counter++;
        }

        else if ($('#Option2').is(':checked')) {
            answers["Q" + counter] = 2;
            counter++;
        }

        else if ($('#Option3').is(':checked')) {
            answers["Q" + counter] = 3;
            counter++;
        }

        else {
            alert("Please make your selection before continuing!");
        }

        // this checks if there are any questions left, otherwise it goes to the result screen
        if (allQuestions[counter]) {
            qload(counter);
        }
        else {
            result();
        }
    });
}

welcome();

});

Answer 1

1) 不能使用字符串作为索引来引用数组元素 (answers["Q"+ i])。您必须使用数字作为数组索引，或者使用对象而不是数组。

2) 不要使用 .attr() 方法修改 DOM 属性，例如“checked”。使用.prop()方法代替。所以你必须替换这个片段:

if (answers["Q" + i]) {
    $("#Option" + i).attr("checked","checked");
}

else {
    $("#Option" + i).removeAttr('checked');
}

具有以下内容:

$("#Option" + i).prop("checked", Boolean(answers["Q" + i]));

3)你获取用户答案值(value)的方式非常麻烦而且奇怪。 这段代码:

    if ($('#Option0').is(':checked')) {
        answers["Q" + counter] = 0;
        counter++;
    }

    else if ($('#Option1').is(':checked')) {
        answers["Q" + counter] = 1;
        counter++;
    }

    else if ($('#Option2').is(':checked')) {
        answers["Q" + counter] = 2;
        counter++;
    }

    else if ($('#Option3').is(':checked')) {
        answers["Q" + counter] = 3;
        counter++;
    }

    else {
        alert("Please make your selection before continuing!");
    }

可以替换为以下内容:

var oEl = $('input:radio[name=radio]:checked');
if (oEl.length) {
    answers[counter] = parseInt(oEl.val());
    counter++;
}
else {
    alert("Please make your selection before continuing!");
}

还需要对单选按钮的 html 代码进行以下修复:

<input type="radio" name="radio" id="Option0" value="0" />
<label for ="Option0">Option0</label>

加上一些其他更改...

所以总代码更新:

$(document).ready(function () {
var allQuestions = [
    {question: "Who is Prime Minister of the United Kingdom?",
        choices: ["David Cameron", "Gordon Brown", "Winston Churchill", "Tony Blair"],
        correctAnswer: 0},
    {question: "Which color has the sky?",
        choices: ["Grey", "Black", "Blue", "Green"],
        correctAnswer: 2},
    {question: "What's on the chain?",
        choices: ["Monster", "Magician", "Bull", "Skull"],
        correctAnswer: 3}
];

var counter = 0; // Question No. currently processed
var answers = new Array(); // Array of the choices the player made

$('#back').click(function(){
    counter++;
    quiz();
});

// update Back button appearance
function updateBackBtn() {
    if (counter > 0)
        $("#back").show();
    else
        $("#back").hide();
}

// set current question
function qload(counter) {
    $("title").text("Question No ");
    $("#question").text(allQuestions[counter].question);
    updateBackBtn();
    for (var i = 0; i < allQuestions[counter].choices.length; i++) {
        $('label[for=Option' + i + ']').html(allQuestions[counter].choices[i]);

        $("#Option" + i).prop("checked", Boolean(answers[i]));
    }
};

// this is the result screen giving the final amount of points
function result() {
    $("title").text("Your Results");
        var points = 0; // Total points currently reached by the player
    for (var i = 0; i < allQuestions.length; i++) {
        if (allQuestions[i].correctAnswer == answers[i]) {
            points++;
        }
        $("#result").show().text("CONGRATULATIONS! You answered " + points + " out of " + allQuestions.length + " correct!");
        $(".qbox").hide();
        console.log(answers);

    }
}

function welcome() {
    // this is the welcome screen inviting to start the quizz
    $("title").text("Welcome to the JQuery QuizY");
    $(".qbox").hide();
    $("#result").append().html("Random");
    $("#result").append().html("<p id='start'>Start</p>");
    $("#start").on('click', function () {
        quiz();
    });
}

function quiz() {
    $("#start, #result").hide();
    $(".qbox").show();
    qload(counter);
    $("#next").on('click', function () {
        // get an input element containing selected option (answer)
        var oEl = $('input:radio[name=radio]:checked');
        // if such input element exists (any answer selected)
        if (oEl.length) {
            answers[counter] = parseInt(oEl.val());
            counter++;
        }
        else {
            alert("Please make your selection before continuing!");
        }

        // this checks if there are any questions left, otherwise it goes to the result screen
        if (counter < allQuestions.length) {
            qload(counter);
        }
        else {
            result();
        }
    });
}

welcome();

});