I want to develop a social media website. So can anyone tell me the what are the programming languages needed for it? I have already included php, javascript and html.
Can you suggest me with any powerful js library?

I took a quick look at Humhub which is Open Source and uses the following languages:

PHP 90.7% JavaScript 7.1% Less 1.2% CSS 0.9% HTML 0.1% Batchfile 0.0%

Looks like you'll be doing a lot of PHP and for the database, your choice.

You typically either write in PHP or in a backend javascript library (node.js), but not both. PHP is considered a little more archaic nowadays, but many open source social platforms happen to be written in it.

An example of a powerful, open-source Javascript-based social platform is Discourse. Of course no PHP required there.

As I have worked on projects that used JavaScript (JS) it has always amazed me how poorly the equality == operator works. For reference read https://algassert.com/visualization/2014/03/27/Better-JS-Equality-Table.html which tries to say "it isn't that bad." I love the first graphic:
d1.png
Later we see the less than operator isn't much better:
d2.png

So if you decide to go with JavaScript, pay attention to these areas or you'll suffer later.
Here's a rearranged table for equality. These tables remind me of what we might see in Game Of Life displays.
d3.png

A social media site needs high functionality and an easy-to-interact user interface to attract the audience on the web. React.JS library and PHP language have emerged as the most powerful open-source tools for building social networking sites. You can learn about the React.JS library for the front end and PHP as a server scripting language for creating the site's back end.

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