JavaScript implements the feature of the Select All option box and the function of the mouse cursor in the drop-down box--javascript instance collection (beginner)

There are some forums where the selection box will appear in the background editor of the article.

1. Implement the option box select all and deselect all functions:

Code implementation:

<! DOCTYPE html>
　2. Mouse clicks the function of the drop-down box: The function of the delay timer is used here
Code implementation:
<! DOCTYPE html>
　　
JavaScript implements the feature of the Select All option box and the function of the mouse cursor in the drop-down box--javascript instance collection (beginner)