Скачать или смотреть How to Fix the Issue of input Value Not Changing in JavaScript

Learn how to correctly update the value of an HTML input field using JavaScript, ensuring smooth functionality in your web applications.
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This video is based on the question https://stackoverflow.com/q/62718796/ asked by the user 'Croximo Crox' ( https://stackoverflow.com/u/13846410/ ) and on the answer https://stackoverflow.com/a/62718938/ provided by the user 'D. Pardal' ( https://stackoverflow.com/u/9253414/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Fix the Issue of input Value Not Changing in JavaScript

In the world of web development, it’s common to encounter various issues while working with user interface elements like forms and inputs. One such problem is when the value of an input field doesn't seem to update as expected. If you've ever found yourself in this situation, you're not alone! In this post, we’ll take a closer look at a specific case where the input value remains unchanged, and how to resolve it.

The Problem

You may have encountered the following piece of code in your web project:

[[See Video to Reveal this Text or Code Snippet]]

And the corresponding JavaScript:

[[See Video to Reveal this Text or Code Snippet]]

Now, you expect the input value to change to 'newtext' after 3 seconds when you type something in the input field. However, it doesn't happen. Why?

Understanding the Issue

The core of the issue lies in how JavaScript handles data types. In this case, the value of an HTML input element is treated as a primitive value (a string). Here’s what’s happening:

When you assign var textinput = document.getElementById('textinput').value;, you're copying the current value of the input field into the variable textinput.

Primitives are passed by value, not by reference. That means any changes you make to the variable textinput will not affect the original input element.

As a result, when you attempt to change textinput within the setTimeout, you're only changing the value of the variable, not the input field itself.

The Solution

To fix this issue, you need to manipulate the input element directly rather than copying its value into a variable. Here’s how to do it:

Modify the way you retrieve the input element:

Instead of storing the input's value in a variable, store a reference to the input element itself.

Update the input value directly:

Here's the corrected code:

[[See Video to Reveal this Text or Code Snippet]]

With the updated JavaScript, the textChanger function now directly changes the value of the inputElement object. Therefore, after 3 seconds, the input field will properly display 'newtext'.

Complete HTML Example

Here’s what the complete HTML and JavaScript should look like:

[[See Video to Reveal this Text or Code Snippet]]

JavaScript (main.js):

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Understanding how JavaScript handles primitives and objects is key to ensuring that your code functions as intended. By directly manipulating the DOM element instead of working with a copy of its value, you can easily avoid issues like the one we discussed.

Keep this in mind when developing your web applications, and feel free to reach out with any questions!