Verifying if a dropdown option has been chosen through validation in JavaScript

Currently, I am working on implementing a validation block in my JavaScript code to ensure that users have selected a value before proceeding. If a value is not selected, I want to display a pop-up message prompting them to do so.


function validate(form) {
    var success = true;
    var message = "";

    if (form.dropdown.selectedIndex == 0) {  
        form.save.disabled=true;

        if (0 < message.length) {
            message += "\n"; 
        }
        
        message += "Please select a dropdown value.";
    }

    if (0 < message.length) {
        alert(message);
        success = false;
    }

    return success;
}

Whenever I click the Save button, this function is called. However, I haven't been able to identify any errors in the logs. Can someone please point out what I might be doing incorrectly here? Alternatively, could you provide guidance on the correct approach to validating whether a user has indeed selected a value before allowing them to save?

Thank you!

Answer №1

In case no option is chosen, the select element's selectedIndex will show as -1. It is recommended to have at least one option marked as selected, so you always know which option is the default (if not, user agents might choose the first option by default).

Therefore, the condition:

if (form.dropdown.selectedIndex ==  0 )  {  

will only be true if the first option is selected. To avoid this ambiguity, either compare against -1 or set the first option as selected by default, like this:

<select name="dropdown" ...>
  <option selected value="default">Please select an option
  ...
</select>

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