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javascript - Populate Drop Down List Box with values from array - Stack Overflow

admin2025-03-13  0

I have a requirement to populate a drop down list box in my form with human races. I believe I've done it correctly but I get an error that says Error: Unable to get property 'appendChild' of undefined or null reference

What am I doing wrong?

HTML: 

<!DOCTYPE html />
<html>
<head>
    <title></title>
    <link rel="stylesheet" type="text/css" href="TheCSS.css" />
    <style type="text/css">
        .style1 {
            height: 26px;
        }
    </style>
</head>

<body>
    <script type="text/javascript" src="C:\Users\Marc\Desktop\JavaScript     Projects\TheJavaScript.js"></script>
    <center>
        <table class="style1">
            <tr>
                <td colspan="4">
                    <center>
                        <h1><b>New Hire Form</b></h1>
                    </center>
                </td>
            </tr>
            <tr>
                <td id="subHeader" colspan="4"></td>
            </tr>
            <tr>
                <td class="style3">First Name</td>
                <td class="style2">
                    <input type="text" id="FirstName" onchange="return LastName_onchange()" />
                </td>
                <td class="style4">Last Name</td>
                <td>
                    <input id="LastName" type="text" onchange="return FirstName_onchange()" />
                </td>
            </tr>
            <tr>
                <td class="style1">Sex</td>
                <td class="style1">Male
                    <input id="Radio1" checked="true" name="R1" type="radio" value="M" />&nbsp;&nbsp;&nbsp; Female
                    <input id="Radio1" checked="true" name="R1" type="radio" value="F" />
                </td>
                <td class="style1">Race</td>
                <td class="style1">
                    <select id="RaceDropDown" name="D1"></select>
                </td>
            </tr>
            <tr>
                <td class="style3">&nbsp;</td>
                <td class="style2">&nbsp;</td>
                <td class="style4">
                    <input type="button" id="myButt" value="Submit Entry" onclick="return      myButt_onclick()" />
                </td>
                <td>&nbsp;</td>
            </tr>
        </table>
    </center>
</body>
</html>

JavaScript:

var select = document.getElementById('RaceDropDown');
var options = ["Asian", "Black"];
var i;
for (i = 0; i < options.length; i++) {
    var opt = options[i];
    var el = document.createElement("option");
    el.textContent = opt;
    el.value = opt;
    select.appendChild(el);
}

function LastName_onchange() {
    var LastName = document.getElementById('LastName').value;
    var FirstName = document.getElementById('FirstName').value;
    document.getElementById('subHeader').textContent = FirstName + " " + LastName + " " + new Date();
}

function FirstName_onchange() {
    var LastName = document.getElementById('LastName').value;
    var FirstName = document.getElementById('FirstName').value;
    document.getElementById('subHeader').textContent = FirstName + " " + LastName + " " + new Date();
}

CSS:

#subHeader
{
    text-align: right;   
}

I have a requirement to populate a drop down list box in my form with human races. I believe I've done it correctly but I get an error that says Error: Unable to get property 'appendChild' of undefined or null reference

What am I doing wrong?

HTML: 

<!DOCTYPE html />
<html>
<head>
    <title></title>
    <link rel="stylesheet" type="text/css" href="TheCSS.css" />
    <style type="text/css">
        .style1 {
            height: 26px;
        }
    </style>
</head>

<body>
    <script type="text/javascript" src="C:\Users\Marc\Desktop\JavaScript     Projects\TheJavaScript.js"></script>
    <center>
        <table class="style1">
            <tr>
                <td colspan="4">
                    <center>
                        <h1><b>New Hire Form</b></h1>
                    </center>
                </td>
            </tr>
            <tr>
                <td id="subHeader" colspan="4"></td>
            </tr>
            <tr>
                <td class="style3">First Name</td>
                <td class="style2">
                    <input type="text" id="FirstName" onchange="return LastName_onchange()" />
                </td>
                <td class="style4">Last Name</td>
                <td>
                    <input id="LastName" type="text" onchange="return FirstName_onchange()" />
                </td>
            </tr>
            <tr>
                <td class="style1">Sex</td>
                <td class="style1">Male
                    <input id="Radio1" checked="true" name="R1" type="radio" value="M" />&nbsp;&nbsp;&nbsp; Female
                    <input id="Radio1" checked="true" name="R1" type="radio" value="F" />
                </td>
                <td class="style1">Race</td>
                <td class="style1">
                    <select id="RaceDropDown" name="D1"></select>
                </td>
            </tr>
            <tr>
                <td class="style3">&nbsp;</td>
                <td class="style2">&nbsp;</td>
                <td class="style4">
                    <input type="button" id="myButt" value="Submit Entry" onclick="return      myButt_onclick()" />
                </td>
                <td>&nbsp;</td>
            </tr>
        </table>
    </center>
</body>
</html>

JavaScript:

var select = document.getElementById('RaceDropDown');
var options = ["Asian", "Black"];
var i;
for (i = 0; i < options.length; i++) {
    var opt = options[i];
    var el = document.createElement("option");
    el.textContent = opt;
    el.value = opt;
    select.appendChild(el);
}

function LastName_onchange() {
    var LastName = document.getElementById('LastName').value;
    var FirstName = document.getElementById('FirstName').value;
    document.getElementById('subHeader').textContent = FirstName + " " + LastName + " " + new Date();
}

function FirstName_onchange() {
    var LastName = document.getElementById('LastName').value;
    var FirstName = document.getElementById('FirstName').value;
    document.getElementById('subHeader').textContent = FirstName + " " + LastName + " " + new Date();
}

CSS:

#subHeader
{
    text-align: right;   
}
  • javascript
  • html
  • arrays
  • list
  • drop-down-menu
Share Improve this question edited Aug 17, 2013 at 5:07 rink.attendant.6 46.3k64 gold badges110 silver badges157 bronze badges asked Aug 17, 2013 at 3:37 mwilsonmwilson 13k10 gold badges62 silver badges102 bronze badges 6
  • seems to work fine mate (fiddle). When is the script being called? As a side, i<options.length is enough because the array Index starts with 0. – Harry Commented Aug 17, 2013 at 3:40
  • I'm calling the script in the body of the HTML. – mwilson Commented Aug 17, 2013 at 3:47
  • Is it after the code for the element RaceDropDown or before it? – Harry Commented Aug 17, 2013 at 3:49
  • I'm calling it before it. – mwilson Commented Aug 17, 2013 at 3:52
  • The script should be called after the element is created, else it would not be able to find the element when it is being executed. can you move this script to just before the </body> tag? – Harry Commented Aug 17, 2013 at 3:57
 |  Show 1 more ment

2 Answers 2

Reset to default 3

Change this:

for (i = 0; i <= options.length; i++)

to 

for (i = 0; i < options.length; i++)

Just need to do < . not <=

As mentioned in my ments, the script should be called after the element is created. If not, the script would throw an error because it will not find the select element to add options.

Please create a function for populating the drop-down and call it onload like the below:

function popDropDown() {
    var select = document.getElementById('RaceDropDown');
    var options = ["Asian", "Black", "White"];
    var i;
    for (i = 0; i < options.length; i++) {
        var opt = options[i];
        var el = document.createElement("option");
        el.textContent = opt;
        el.value = opt;
        select.appendChild(el);
    }
}

window.onload = popDropDown;

As an aside, in the for loop i < options.length is enough instead of i <= options.length.

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