How to Get the Value of a Select Element Before It Changes in JavaScript?

Retrieving the Value of a Select Element Before Change

JavaScript provides various event listeners that allow developers to respond to user interactions. One common need is the ability to retrieve the value of a (dropdown) element before it changes. This technique is especially useful when working with multiple dropdowns on a single page, where you may need to retain the previous value for comparison.

To accomplish this, we can utilize a combination of the focus and change events. The following code snippet demonstrates how:

(function() {
  var previous;

  $("select").on("focus", function() {
    // Store the current value on focus and on change
    previous = this.value;
  })
  .change(function() {
    // Do something with the previous value after the change
    console.log(previous);

    // Update the previous value with the new selection
    previous = this.value;
  });
})();

This code employs an anonymous self-executing function to avoid polluting the global namespace. It attaches an event listener to all elements on the page. Upon focusing on any dropdown, it stores the current value. When the selection is changed, it logs the previous value and updates it with the new selection.

This approach allows you to work with multiple dropdowns on the same page and retrieve their previous values before each change. You can integrate this code into your project to enhance the user experience and facilitate more advanced functionality involving dropdown inputs.

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