Using JavaScript to extract information from a dropdown menu

Currently, I am working on a project that involves reading values from a dropdown box on a webpage and alerting the selected value. Below is the code I have written for this task.

JavaScript

function main(input)
{
    value = getValue();
    alert(value);
}

function getValue()
{
    var len = document.form1.values.length
    var chosen = ""

    for (var i = 0; i < len; i++) {
        if (document.form1.values[i].selected) {
            chosen = document.form1.values[i].value
        } 
    }

return chosen;
}

HTML

    <!DOCTYPE HTML>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
        <title>Shopping Cart</title>
        <link href="style.css" title="Style" rel="stylesheet" type="text/css">
        <script src="javascript/js.js" type="text/javascript"></script>
    </head>

    <!-- Start content -->
    <body>
        <div id="wrapper">
            <div id="header">
                <h1>Kyle's Legit Toys</h1>
                <h2>We are more legit than 10th.exe</h2>
                <h3>#SoundsLegit</h3>
            </div>

            <div id="menu">
                <a href="#">Home</a>
                <a href="http://itsuite.it.brighton.ac.uk/ks339/sem2/clientValidation.htm">Client Validation</a>
            </div>

            <div class="first">
                <p>Wickedy Walker</p>
                <img src="i/car.jpg" width="85%" height="85%" alt="Car" title="#CoolCar">
                <p>Cost: £30 per item</p>

                <form name="form1" method="POST">
                    <select name="values" onchange="main()" >
                        <option value="1">1</option>
                        <option value="2">2</option>
                        <option value="3">3</option>
                        <option value="4">4</option>
                        <option value="5">5</option>
                        <option value="6">6</option>
                        <option value="7">7</option>
                        <option value="8">8</option>
                        <option value="9">9</option>
                    </select>
                </form>
            </div>

            ...

            <div id="footer">
                <p>Kyle Strudwick - ks339 - StudentNumber</p>
                <p>Some copyright stuff</p>
            </div>
        </div>
    </body>
</html>

Error in Chrome

Firebug

Thank you! When providing feedback, please explain any mistakes I made, why they were incorrect, and the proper way to address them.

Thanks

Answer №1

Make a slight adjustment to your HTML code:

<select name="values" onchange="main(this)" >
    <option value="1">One</option>
    <option value="2">Two</option>
    <option value="3">Three</option>
    <option value="4">Four</option>
    <option value="5">Five</option>
    <option value="6">Six</option>
    <option value="7">Seven</option>
    <option value="8">Eight</option>
    <option value="9">Nine</option>
</select>

Additionally, update your function like so:

function main(input)
{
    var text = input.options[input.selectedIndex].text; // returns the selected text (e.g. One, Two)
    var value = input.value; // returns the selected value (e.g. 1, 2, 3)
}

Changes Made - I have modified the onchange attribute in the HTML from main() to main(this). This alteration ensures that the current select list object is passed to the main function, making it easier to access and manipulate the specific select list that triggered the change.

Function Functionality - by passing the actual select list object as input, we can directly retrieve the selected option using input.selectedIndex and its corresponding value with input.value.

The previous use of document.forms1 was not effective due to multiple forms with the same name on the page. By simplifying to one form surrounding the content, the functionality remains intact without relying on multiple forms.

Additional Tip - Consider consolidating multiple redundant forms into a single form for improved efficiency while utilizing the above method to handle value changes smoothly.

Check out this demonstration showcasing the updated implementation

Answer №2

All of your forms are labeled as form1, which means that when you use document.form1, you are actually retrieving an array of <form> elements. To access them individually, you can use document.form1[0].values for the first form. If you want to create a versatile function, make sure to pass in the current select element (the one triggering the onchange event) so that your function knows which specific form1 to work with.

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