How to play minecraft on the pc with no download for free?

No. It's a downloaded game and you need an account that you have to purchase.

It's a downloaded game. No download, no game.

Nope

There's a demo on minecraft.net other than that, you have to pay for an account.

If you run Minecraft off a flashdrive.

The original "Classic" Version was available online for free until around 2012 when security issues w/ java made that version of the game practically unplayable & it's no longer supported.

Right now, you'll have to download it (as there's no online-browser version available) & pretty much purchase it if you want access to all the versions of game (from pre-alphas to present). You can purchase a USB flash drive with Minecraft preinstalled for ~$50 ("Premium" user acct / Game License NOT INCLUDED) to eliminate or reduce the need for downloads.