SciChart.js ships with ~60 JavaScript Chart Examples which you can browse, play with, view the source code and see related documentation. All of this is possible with the SciChart.js Examples Suite, which ships as part of the SciChart.js SDK
Demonstrates how to create crosshairs on mouseover using SciChart.js, High Performance JavaScript Charts
Demonstrates using the CursorModifier, part of the ChartModifier API, to add a cursor and tooltips which tracks the mouse.
This can be used to add Tooltips to a JavaScript chart as well as draw cursors (crosshairs) and axis labels values as the user moves the mouse.
The hitTest function accepts parameters to control the hit-test logic. See the documentation on Hit-Testing for more info!