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Learn how to manage stock values dynamically using JavaScript and HTML input fields to reflect changes accurately and revert them when necessary.
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This video is based on the question https://stackoverflow.com/q/64904553/ asked by the user 'NewbieKid' ( https://stackoverflow.com/u/9309671/ ) and on the answer https://stackoverflow.com/a/64904901/ provided by the user 'York Chen' ( https://stackoverflow.com/u/2207323/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Dynamically Adjust Item Stocks with JavaScript and HTML Input Fields

Managing stock levels in web applications is crucial for many businesses operating online. One common task is to allow users to adjust stock levels interactively through input fields. In this post, we’ll tackle a specific challenge: how to add a specified amount to an item's stock and revert back to the original stock if the user clears the amount entered.

The Problem

When you enter an amount in an input box to increase the stock of an item, it should reflect correctly by adding that value to the original stock. But what if the user decides to remove the amount they entered? In that case, the stock needs to return to its previous value.

You might have tried implementing it using JavaScript and your HTML input fields but ended up facing issues, such as inaccurate calculations and errors like 'NaN' cropping up as soon as the user clears their input.

The HTML Structure

Before diving into the solution, let's take a look at the HTML structure we're working with:

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

The first input field (# Stocks) displays the current stock value pulled from the database.

The second input field (# addNum) is where users enter the amount they wish to add to the stock.

The Solution

To accomplish the task at hand, we’ll implement a JavaScript function that performs the following operations:

Retrieve the original stock value from the database.

Listen for user input on the second input field and dynamically adjust the stock value.

Handle cases where the input is cleared and revert the stock to its original value.

Step 1: Initialize Original Stock Value

When loading the app, retrieve the original stock value from your database and store it in a variable:

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

Step 2: Listening for User Input

Using jQuery, set up an event listener to react to any changes in the # addNum input field:

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

Breakdown of JavaScript Functionality

Retrieving Stock Values: We use parseInt() to convert string representations of numbers into integers.

Checking Input Validity: The isNaN(input1) function checks if the user’s input is a number. If the input is cleared (which results in NaN), we set the stock value back to originalValue.

Updating the Stock Field: Finally, we update the value of the # Stocks input field with the newly calculated stock amount.

Conclusion

By following these steps, you can implement a dynamic stock management system that correctly reflects user input, keeping your inventory accurate and user-friendly. Implementing event listeners alongside proper error handling ensures that your users have a smooth experience while interacting with the system.

Feel free to adapt and extend this basic setup to fit your specific application needs!