Are you connecting via the USART USB connector rather than the USB that goes straight to the STM32 chip? Often if you use the USART it just ends up being so slow that the Web IDE times out while waiting for a response.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Are you connecting via the USART USB connector rather than the USB that goes straight to the STM32 chip? Often if you use the USART it just ends up being so slow that the Web IDE times out while waiting for a response.