How to determine whether a control is available in jquery

jQuery is a very popular JavaScript library that makes it extremely easy to implement interactivity in web pages. During the development process, sometimes we need to determine whether a control can be used for the next operation, which can improve the usability, readability and maintainability of the code. Therefore, in this article, the author will share how to determine whether a control is available in jQuery.

1. The status of the control

Before we begin, we must understand the status of the control. Whether it is a text box, a drop-down box or a check box, their states generally include the following three states:

1. Available state (enabled): The control can be operated, and the user can input, select, and Click and wait.
2. Disabled state (disabled): The control cannot be operated and the user cannot perform any operations on it.
3. Read-only state (readonly): The control cannot be edited, but operations such as selection and clicking can be performed.

Through the above description, we can see that the read-only state and the available state are different. In the read-only state, the control can be used, but the user cannot edit it and can only perform operations such as selection or clicking. To determine whether a control is read-only, we can determine whether the readonly property of the control is true. The available and disabled states of controls are relatively similar. To avoid confusion, we call the available state of the control "enabled" and the disabled state of the control "disabled".

2. Attr method

In jQuery, we can use the attr() method to get or set element attributes. The attr() method can obtain the attribute value of one or more matching elements. If the attribute does not exist, it returns undefined.

Therefore, we can use the attr() method to determine whether a control is available.

As shown in the following example:

<input type="text" id="text1" disabled="disabled" value="disabled">
<input type="text" id="text2" value="enabled">

In HTML, we declare two text boxes, namely text1 and text2. text1 is set to the disabled state and text2 is set to the enabled state. Then, in jQuery, we can use the following code to determine whether these two controls are available:

if($('#text1').attr('disabled')) {
    alert('text1 is disabled.');
} else {
    alert('text1 is enabled.');
}

if($('#text2').attr('disabled')) {
    alert('text2 is disabled.');
} else {
    alert('text2 is enabled.');
}

After running the code, we will find that the first text box determines whether its disabled attribute is true. Whether it is disabled, and the second text box does not have a disabled attribute, so it returns undefined. Based on this result, you can determine whether the text box is enabled.

3. Prop method

After jQuery version 1.6, jQuery introduced the prop() method. Compared with the attr() method, the prop() method can get or set the attribute value of the element, but only for the DOM attribute of the element.

The enabling or disabling of a control is a state of the DOM attribute, so we can determine the state of the control through the prop() method.

As shown in the following example:

<input type="text" id="text1" disabled="disabled" value="disabled">
<input type="text" id="text2" value="enabled">

You can use the following code to determine whether the two text boxes are enabled:

if($('#text1').prop('disabled')) {
    alert('text1 is disabled.');
} else {
    alert('text1 is enabled.');
}

if($('#text2').prop('disabled')) {
    alert('text2 is disabled.');
} else {
    alert('text2 is enabled.');
}

In the above code, if a When the control is enabled, the prop() method returns false. If it is disabled, the prop() method returns true. In actual development, we can use the prop() method to more easily determine the status of the control.

4. Summary

To determine whether a control is available in jQuery, we can use the attr() method or the prop() method. The attr() method determines whether the control is available by getting the attribute value of the element, while the prop() method can return the DOM attribute of the element and also determine whether the control is available. Through the method introduced in this article, the status of a control can be easily determined. In actual development, we can flexibly use these methods according to specific needs.

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