Indeed, JSX can be traced back to Facebook's idea of XML syntax on top of PHP called XHP [1][2]. It was never adopted by the community and did not break out of

Indeed, JSX can be traced back to Facebook's idea of XML syntax on top of PHP called XHP [1][2]. It was never adopted by the community and did not break out of FB's custom PHP runtime called HHVM. [1] https://www.facebook.com/notes/facebook-engineering/xhp-a-new-way-to-write-php/294003943919/ [2] https://docs.hhvm.com/hack/XHP/introduction