syntastic plugin checks after saving. Can I check as I type the code?
judging by the documentation for the plugin, this is not possible. And this is logical – the plugin uses the capabilities of compilers / interpreters to check the validity. Launching any interpreter and checking the syntax is not a matter of seconds. And Vim, in order to provide the specified functionality, will have to save a buffer for each press and run the checker. And a delay of even 0.05 seconds between clicks will be very annoying.