Page not Found
The page you were trying to access does not exist anymore, or has never existed. If you are looking for a documentation page you should be redirected automatically, unless you have disabled JavaScript in your browser. If so, add "/0.3" immediately after "api" in the url:
https://citation.js.org/api/0.3/index.html
For documentation of 0.5 and later versions, check out https://citation.js.org/api/0.7