Default bond setting. It is also a combo button: the other types of bonds can be selected from a sub-menu, after clicking on the black triangle in the lower-right corner of the button.

What kind of bonds are available in Marvin JS?

You can also use keyboard shortcuts to choose a bond type to connect two atoms or alter an already existing bond. See the complete list of chemical bonds available in Marvin JS and their respective keyboard shortcuts in the table below.

How to draw a bond:

Selecting a bond type and clicking or dragging on the canvas will create a new bond with the default length and with carbon atoms on both ends.
You can also draw a new bond by dragging from an already existing atom or clicking on it with an active bond tool.

Watch how to draw Position variation bond.