GoJS

Pros: - performance
- ease of development
- it's easy to extend components
- multiple built-in layouts
- multiple ready to use functionalites helping in diagramming tasks
- many component examples on their main page
- great support

Cons: - complex node templates are sometimes hard to build
- since it uses canvas to render a diagram, it's not possible to style objects on a diagram with css

Overall: We have used GoJS extensively since 2012. It helps us deliver complete data visualization and process modeling projects to our customers.
We tested the library in simple diagramming components and complex projects with custom graph functionalities. What's more, we even managed to implement a real-time collaboration diagram using GoJS, among others technologies.

What we like the most about GoJS is how much freedom it gives to the developer. Its functionalities have never restricted us. Every module and tool can be extended, so achieving custom features is almost always possible.

GoJS also delivers many ready-to-use components and functionalities like layouts, mouse tools, and animations. We like its focus on details: you need to calculate the nearest line point to your current object? They have a ready-to-use function; do you need to find all elements in a certain radius around the mouse cursor? They've got you covered. We often find ourselves surprised by how many features are already implemented. Tasks that we estimated to take several hours are implemented in an instant.

One of the essential advantages of GoJS is its performance. For many projects we implemented, it was the main reason we chose this technology. The library makes it possible to create large, complex, dynamic diagrams with thousands of objects. Every user's action like dragging, dropping, panning is still smooth. Using some techniques like virtualization, it is even possible to render humongous graphs having hundreds of thousands of objects and connections.

Of course, there is also room for improvement for this technology. Creating and maintaining complex node templates can be tricky. Since it operates on canvas, it's not easy to take advantage of HTML inputs/charts on a diagram. Some layouts implementations aren't optimal. Those things could be better but aren't showstopper in any way. Thanks to the flexibility of the library, we can always find a workaround, integrate 3rd party library, or just email library creators who have a perfect response time.

If anyone is interested what are GoJS capabilities and want to see its usages outside of their main page, we invite you to check out SynergyCodes' main page (synergycodes.com) and our Dribbble (dribbble.com/SynergyCodes)