How to run "brew" command in windows..?

As mentioned in the comments, Homebrew is a package manager for OSX, much like Aptitude in linux. You can't install Homebrew on Windows and never will be able to so you need to find a new way to accomplish what you are doing. I think you're trying to work with Google's V8 Javascript engine so why not try: https://github.com/phpv8/v8js

Edit: Homebrew is also usable on Windows Subsystem for Linux (WSL) since version 2.0.0 (released February 2019), as detailed by @VonC's answer below. The instructions for installation/use are available at:

• https://docs.brew.sh/Homebrew-on-Linux

---

Homebrew is MacOS only command line installer application and it doesn't exist for Windows.

The Windows alternatives are:

• Chocolatey
• Npackd
• Scoop
• OneGet for Windows 10

Source: https://laracasts.com/discuss/channels/laravel/homebrew-install-on-windows-os

It shows "'brew' is not recognized as an internal or external command" in windows command prompt.

Not anymore, 19 months later (Feb. 2019, compared to July 2017)

At least, not on Windows 10, in a WSL (Windows Subsystem for Linux) session.
As mentioned by Mike McQuaid

Homebrew 2.0.0 has been released (at @FOSDEM!) with official Linux and Windows 10 WSL support, brew cleanup running automatically (opt-out with HOMEBREW_NO_INSTALL_CLEANUP), no more options in Homebrew/core and no longer running on OS X 10.8 and older.

See Homebrew 2.0.0.

“Homebrew on Linux” is called “Linuxbrew”.
You can install it in your home directory, so it does not require sudo, and use it to install software that your host distribution’s package manager does not provide. Linuxbrew uses its own repository for formulae: Linuxbrew/homebrew-core.

So again, this is not native Windows support, but Linux (through the WSL layer, on Windows 10).