DSA is necessary before starting web development ?

No, not at all.

The obvious answer is no! You don't need to have Dsa Knowledge to start web development .... After the frontend part when you would be starting with a programming language for lets say backend then fair idea of DSA could help in logic building...

Note that we are talking about Dsa not Competitive Coding !

No, what even is DSA..

AS I am learning javascript now .can I the start my DSA in javascript, is it best option to start in javascript if yes... Could you please suggest me some free platform for DSA in javascript

yes for optimize code