js or php?

why not learn both ? from personal experience don't go for one language try to learn other as well. JS, PHP or Python they all are scripting language so if you learn one language better you can easily change with others. Second is what is your priority if you are learner learn both , if you are job seeker learn JS because it have more jobs & better salary and last if you have some personal project they try to find real need of the project.

if your looking for a job, go for JS!

From what I know for those who work in the industry, javascript is the most widely used, and PHP is frown upon.

JS is better but as you wish

From my own experience, if you can do either javascript or PHP, you can do both of them. These languages have similar syntax and the same scripting language and style, so just choose either one, and you're good to go.
My favourite language is javascript, because you can do mobile, frontend, and also backend with just one language

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.

If you had to pick just one, JS wins hands down as it can handle both front end and back end with NodeJS

If you want to land yourself in a professional place then my suggestion is php where you can get good placement in a prestigious it company with good salary

It depends on what you want to do.. I would say both work together