Imagine you're building a web application and you want to capture the old value of a text box when a user makes changes. This can be super useful for tracking changes, validating inputs, or even triggering certain actions based on the previous value. In this article, we'll walk through how to achieve this using the onchange event in JavaScript.
First things first, let's set up a simple HTML page with a text box where we can capture the old and new values. Here's a basic example to get us started:
<title>Get Old Value with Onchange Event</title>
let oldValue = document.getElementById('myInput').value;
function handleInputChange() {
let newValue = document.getElementById('myInput').value;
console.log('Old Value:', oldValue, 'New Value:', newValue);
oldValue = newValue;
}In this code snippet, we have an input element with the ID `myInput` and an initial value of "Initial Value". We've also set up an `onchange` event that calls the `handleInputChange` function whenever the input value changes.
Inside the `handleInputChange` function, we capture the new value of the input and log both the old and new values to the console. We update the `oldValue` variable with the new value so that it reflects the most recent input.
Now, whenever a user types something in the text box and moves away from it, the `handleInputChange` function will be triggered, showing the old and new values in the console.
Feel free to customize this code snippet to fit your specific requirements. You can add validation logic, perform calculations based on the old and new values, or update other parts of your application dynamically.
Remember, the `onchange` event is triggered when the input field loses focus after its value has been changed. This means that if a user changes the input but doesn't move away from it (by clicking elsewhere or pressing the Tab key), the event won't be fired.
In conclusion, getting the old value with the `onchange` event in a text box is a handy technique to enhance user interactions and improve the functionality of your web applications. Have fun experimenting with this approach and see how it can add value to your projects!