Tether is a JavaScript library for making an element stay next to another element on the page

Tether is a small, focused JavaScript library for defining and managing the position of user interface (UI) elements in relation to one another on a web page. It is a tool for web developers building features that require certain UI elements to be precisely positioned based on the location of another UI element.

There are often situations in UI development where elements need to be attached to other elements, but placing them right next to each other in the DOM tree can be problematic based on the context. For example, what happens if the element we’re attaching other elements to is fixed to the center of the screen? Or what if the element is inside a scrollable container? How can we prevent the attached element from being clipped as it disappears from view while a user is scrolling? Tether can solve all of these problems and more.