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How to make the select tag expand by default in javascript

PHPz
Release： 2023-04-25 19:00:27
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In HTML, theelement.

Implementation method:

1. Use the autofocus attribute of HTML5

The easiest way is to use the autofocus attribute of HTML5. This attribute can automatically set focus on the specified input box, button, drop-down list and other elements after the page is loaded. To make a Copy after login2. Using JavaScript codeWhen we need to expand theelement when the page loads, the autofocus attribute may not be able to achieve our needs. At this time, we can use JavaScript code to achieve this. The code is as follows:
Copy after login

The above code automatically expands the drop-down list by setting its size (size) to its number of options (length). Of course, you can also use other methods to achieve the same effect, such as setting the options attribute, or using CSS styles, etc.

3. Expandunder specified conditions, such as when an event is triggered, or when a certain value When conditions are met. At this time we need to use JavaScript code to operate. The code is as follows:
Copy after login

The above code listens to the click event ofelements, we need to pay attention to some details:

  1. Using JavaScript code The
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