How does PHP dynamically control the readOnly attribute of HTML form elements?

Use PHP to dynamically control the readOnly attribute of HTML form elements

In web development, dynamically controlling the readOnly attribute of HTML form elements is a common requirement, such as determining whether the input box is editable based on user permissions or specific conditions. This article will analyze a common mistake practice and provide the correct PHP solution.

Many developers try to set readOnly property to true or false directly in HTML tags, for example:

<input type="text" value="<?php echo isset($_GET['userName']) ? $_GET['userName'] : ''; ?>" readonly>

However, this method is ineffective. The control of readOnly property does not depend on true or false values, but whether it exists in the tag. As long as the readonly property exists, the input box will be in a read-only state and the property value does not matter.

The correct way to do this is to dynamically add or remove readonly attributes based on conditions. The improved code is as follows:

<input type="text" value="<?php echo isset($_GET['userName']) ? $_GET['userName'] : ''; ?>" echo isset :>>

This code utilizes PHP's ternary operator: if $_GET['userName'] exists, add the readonly attribute; otherwise, no attributes are added, and the input box remains editable. This server-side processing method is simple and efficient. Although JavaScript can be used to dynamically operate readOnly property, in this case, PHP server-side processing is more direct.

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