How to Repopulate HTML Select Options Without Firing the Change Event with jQuery

When working with multiple HTML select elements in a web application, you may find yourself in a situation where selecting an option in one dropdown affects the options available in another. A common scenario is to make an option available in one select disappear when it is selected in another. However, doing this can inadvertently trigger change events that can complicate your logic. In this post, we’ll tackle how to dynamically repopulate select options without firing the unwanted change events using jQuery.

The Problem

Imagine you have two dropdowns (select elements) that are interdependent. You want to implement a system where selecting an option in one dropdown removes that option from the second dropdown, ensuring that users can’t select the same option from both. However, with the default jQuery behavior, changing the options in one select also calls the change event for that select, which could lead to unexpected behavior in your application.

Example Scenario

Here’s a simple HTML structure to illustrate the dropdowns:

<select id="one">
  <option value="1">one</option>
  <option value="2">two</option>
  <option value="3">three</option>
</select>
<select id="two">
  <option value="1">one</option>
  <option value="2">two</option>
  <option value="3">three</option>
</select>

When you select “one” from the first dropdown (#one), the goal is to remove “one” from the second dropdown (#two). If you then select “two” from #two, the same behavior should occur in reverse.

The Solution

To avoid firing change events while repopulating the options in your selects, you will need a two-step approach: temporarily disconnect the event handlers and use a flag to determine whether the change event should be processed.

Step 1: Modify the JavaScript Logic

Start by setting up your jQuery functions as follows:

$(function () {
    var $one = $("#one");
    var $two = $("#two");

    var selectOptions = [ 
        $("option", $one).clone(), 
        $("option", $two).clone() 
    ];

    var isChanging = false; // Flag to prevent firing change events

    $one.change(function () {
        if (isChanging) return; // Ignore if already changing
        
        isChanging = true; // Set flag before changing options
        var selectedValue = $("option:selected", this).val();
        $two.find("option[value='" + selectedValue + "']").remove();
        repopulateOptions($two, selectOptions[1]); // Restore options
        isChanging = false; // Reset flag
    });
    
    $two.change(function () {
        if (isChanging) return; // Ignore if already changing
        
        isChanging = true; // Set flag before changing options
        var selectedValue = $("option:selected", this).val();
        $one.find("option[value='" + selectedValue + "']").remove();
        repopulateOptions($one, selectOptions[0]); // Restore options
        isChanging = false; // Reset flag
    });

    function repopulateOptions($select, options) {
        options.each(function() {
            if (!$select.find("option[value='" + this.value + "']").length) {
                $select.append(this); // Append only if not already present
            }
        });
    }
});

Step 2: Explanation of Key Components

• isChanging Flag: This boolean flag keeps track of whether the event handlers should be executed or ignored, preventing any accidental event firing during option manipulation.
• Repopulate Function: This function helps resync the selects by restoring previously available options, ensuring the user has access to all choices unless already chosen in the other dropdown.
• Cloning Options: Cloning the original options allows us to maintain a reference to all available choices, making it easier to manage what gets displayed.

Conclusion

Managing interdependent select options can be tricky, especially when aiming to avoid unwanted event triggers. By following the guidelines in this post, you can implement a seamless user experience where select choices dynamically adjust in real-time without any associated issues from event firing. This solution not only protects against unexpected behaviors but also keeps your options clear and users engaged!

If you have any questions or want to share your own experiences with jQuery and dynamic dropdowns, feel free to leave a comment below!