can't save code ESP32 with i2C oLED

@user88194 in your case the problem is var g in init - you're defining it locally, so g won't exist when used in start. Try:

var g;
function start(){
  g.clear();
  g.drawString("test",0,0);
  g.flip();
}
E.on('init', function() { 
  // I2C
  I2C1.setup({scl:D4,sda:D5});
  g = require("SSD1306").connect(I2C1, start);
});