Can i upload a file (big binary) to Flash with certain address in Web Ide?

What device are you using? Bangle.js, or something else?

Honestly I'm not sure you're going to have much luck trying to force the Web IDE in to uploading a file - the file upload there is designed to use Storage.

The best solution is:

• Go to http://www.espruino.com/File+Converter
  
• Upload your file
  
• Choose Base 64 Flash Write as the mode
  
• Copy the code from the text box
  
• Paste it into the REPL of the Web IDE
  
  

And you should be sorted!

If you want to automate it, it should be reasonably easy to mash the File Converter code together with the Web Bluetooth example at http://www.espruino.com/Web+Bluetooth to make a website that will upload directly