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Asked: 2026-05-31T19:16:51+00:00

I have been stuck on this and don’t really know how to go about

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I have been stuck on this and don’t really know how to go about fixing it myself. I’ve tried using firebug and getting parts of it to work, but it’s just so frustrating and time consuming for such a small script. Perhaps I’m using the switch statement wrong…

Essentially I’m making a very simple calculator using an Object for the first time…
Any little bit will help–any push in the right direction 🙂

Thanks so much for reading!

The HTML file is this:

    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>

    <title>Homework 8</title>
        <link href="css/main.css" rel="stylesheet" type="text/css"/>
</head>

<body>
    <div id="calc">
        <p><label for="num1">First Number:<input type="text" id="num1" class="txt" /></label></p>
        <p><label for="num2">Second Number: <input type="text" id="num2" class="txt"/></label></p>
        <p><label for ="add"><input type="radio" name="operation" id="add" value="add"/>Add</label> 
        <label for ="sub"><input type="radio" name="operation" id="sub" value="sub"/>Subtract</label> 
        <label for ="mult"><input type="radio" name="operation" id="mult" value="mult"/>Multiply</label> 
        <label for ="div"><input type="radio" name="operation" id="div" value="div"/>Divide</label></p>
        <p><input type="button" id="calculate" value="Do Calculation"/></p>
    </div>
    <div id="result"></div>
<script type="text/javascript" src="js/hw8.js"></script>
<script type="text/javascript">obj.init();</script>
</body>
</html>

The Javascript file is this short script:

var obj = {

add : document.getElementById("add"),
sub : document.getElementById("sub"),
mult : document.getElementById("mult"),
div : document.getElementById("div"),
num1 : document.getElementById("num1"),
num2 : document.getElementById("num2"),
result : document.getElementById("result"),
calculate : document.getElementById("calculate"),

    init : function(){

        obj.calculate.onclick = obj.resultArea;

    },

    resultArea : function(){

        var num1Value = parseFloat(num1.value);
        var num2Value = parseFloat(num2.value);

        if (!isNaN(obj.num1Value) = true || !isNaN(obj.num2Value) = true){
            alert("Please enter only numbers in the First Number and Second Number fields!");
            return;
        }

        switch(true){
            case obj.add.checked : var ans = (num1Value + num2Value); break;
            case obj.sub.checked : var ans = (num1Value - num2Value); break;
            case obj.mult.checked : var ans = (num1Value * num2Value); break;
            case obj.div.checked && num2Value != 0 : var ans = (num1Value / num2Value); break;
            case obj.div.checked && num2Value = 0 : alert("cannot divide by zero"); break;
        }


        var p = document.createElement("p");
        p.appendChild(document.createTextNode("The answer is" + ans));
        obj.result.appendChild(p);
    },

}
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1 Answer

  1. Editorial Team
    if (!isNaN(obj.num1Value) = true || !isNaN(obj.num2Value) = true)

    Besides the the error due confusing the assignment operator (=) and the equality comparison operator (==) operator this
    is overly complex.

    If not obj.num1Value is not a number is true and not obj.num2alue is not a number is true do?

    • Say what?

    Consider this formulation:

    if ( isNaN(obj.num1Value) || isNaN(obj.num2Value) )

    Ah, if either obj.num1Value or obj.num2Value is not an number do…

    Also you may want to declare the ans and ´p´ variable once at the top of the resultArea function:

    resultArea : function(){
    var ans;
    var p;

    // ...

    switch(true){
        // Note that we removed var keyword! 
        case obj.add.checked : ans = (num1Value + num2Value); break;
            // ..

    Also if you use a line break for each case in the switch statement it becomes much easier to follow
    the control flow:

    switch(true){
        case obj.add.checked :  
            ans = (num1Value + num2Value); 
            break;
        case obj.sub.checked :  
            ans = (num1Value - num2Value); 
            break;
        case obj.mult.checked :  
            ans = (num1Value * num2Value); 
            break;
        case obj.div.checked && num2Value !== 0 : 
            ans = (num1Value / num2Value); 
            break;
        case obj.div.checked && num2Value == 0 : 
            alert("cannot divide by zero"); 
            break;
    }

    You are not you are not covering the scenario where you do not have an answer:

     if ( typeof ans !== 'string') {
    p.appendChild(document.createTextNode("The answer is forever blowing in the wind"));
 }
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