js or php?

Both, In my experience. JavaScript and PHP both are scripting language for web development. Beside web development, JS can be used for Multi-Platform development like mobile, desktop.
With the rise in Front-End Frameworks like (React and Vue), I would recommend you to go with JavaScript (If only you have a single choice). Otherwise, learning one beforehand and being good at it will certainly help you learn the next language in less time frame.