Why does the jQuery change event not trigger when I set the value of a select using val()?

The Core Concept: Browser Behaviour

Standard browser behavior fires a change event when a user selects with the mouse or keyboard. This emphasizes direct user interaction. However, jQuery's .val() behaves differently. This method modifies values but doesn't replicate user interaction.

Ergo, you need to manually trigger the change event to simulate a user-initiated change:

$('#your-selector').val('select-value').trigger('change');


Here, .trigger('change') closely mirrors the user's possible actions by manually announcing a change, sparking any waiting listeners into action!

Improving Experiences: A Reusable Function

Code reuse is a hallmark of efficient programming. Let's define one such function, valAndTrigger(), to simplify this process across your entire application:

$.fn.valAndTrigger = function(value) {
  return this.val(value).trigger('change');
};

// Who's the smart coder now? 👈
$('#select-id').valAndTrigger('new-value');


With this approach, you're killing two birds with one stone: setting the value and triggering the change event in a single method.

Additional Noteworthy Situations

Here are some real-world programming scenarios where the knowledge we just gained produces the optimal results:

• Data Binding: Keeping your model state and UI aligned needs a .change() following every .val().

• Form validation: Manual trigger guarantees form validations apply after field value changes.

• Dynamic UI updates: Manual triggers ensure complete and perfect updates.

The better we understand this behavior, the more reliable and robust our applications behave.