d3. js will stay the state of the art for the at least next five years. The last version came out on March and the API is widely accepted. There is no competitor at the moment which is even close to the functionality Is D3 free to use?
D3 is open-source. So you can work with the source code and add your own features. It works with web standards so you don't need any other technology or plugin other than a browser to make use of D3. D3 works with web standards like HTML, CSS and SVG, there is no new learning or debugging tool required to work on D3 What is D3js used for?