I had forked a the pyflasher repository https://github.com/marcelstoer/nodemcu-pyflasher and make a custom changes for the custom flasher required for SPIFFS flashing, if your interested here is the repository https://github.com/ivanalayan15/nodemcu-pyflasher
Download here
Custom flasher download link : https://github.com/ivanalayan15/JuanFi/blob/master/release/LanBased/ESP8622/NodeMCU-PyFlasher.exe?raw=true
Download JuanFi-FlashFile1.bin at https://github.com/ivanalayan15/JuanFi/blob/master/release/LanBased/ESP8622/JuanFi-FlashFile1.bin?raw=true
- select the file JuanFi-FlashFile1.bin
- make sure the offset is 0x000000
- click Flash Nodemcu and wait to complete
Download JuanFi-FlashFile2.bin at https://github.com/ivanalayan15/JuanFi/blob/master/release/LanBased/ESP8622/JuanFi-FlashFile2.bin?raw=true
- select the file JuanFi-FlashFile2.bin
- make sure the offset is 0x200000
- click Flash Nodemcu and wait to complete