javascript options attribute collection operation code_form effects

Use the following code to access the options in the drop-down box:

If you want to delete option

Mark this option object as null, and this option will be completely removed from the list.
Note: This operation will affect the number of options. Assume that in the above example, you delete option[1], the original option[2] element ('Third option') will become the option[1] element (option elements are pushed up in order).
Create a new option as follows:

The user sees the text and value displayed by the option on the page The value is the VALUE attribute of this option.
When the form is submitted, the VALUE value is passed to the WEB server.
If you want to clear all options in the select box, as follows: