What is the principle behind Bootstrap’s scrollspy?

JavaScript is used to implement the principle of Bootstrap scrollspy.

In Bootstrap, the scrollspy plugin can be used to achieve scroll monitoring. This plugin automatically detects the scrolling position on the page and activates the corresponding navigation links or other elements based on the scrolling position.

The specific implementation principle is as follows:

1. Firstly, you need to define a menu or other element that includes navigation links, and add a data-target attribute to each navigation link with the value being the ID or selector of the target element.
2. After the page has finished loading, initialize the scrollspy plugin with JavaScript. This plugin will automatically scan the navigation links on the page and activate the corresponding link based on the scrolling position.
3. The scrollspy plugin listens for scroll events as the page is scrolled, calculating the position of each target element in relation to the current scroll position. If the current scroll position is within the range of a target element, the corresponding navigation link will be activated.
4. When the active navigation link changes, the scrollspy plugin will trigger the corresponding event, which can be handled with JavaScript to, for example, update the style of the navigation links or perform other tasks.

In conclusion, the principle behind Bootstrap scrollspy is to use JavaScript to monitor the page scroll event, and activate the corresponding navigation link based on the scroll position, thus achieving the scrollspy effect.