Getting I2C on ESP8266 to work

I guess you use the WEBIDE and upload your code, so the time between writeTo and readFrom is different.

To make it equivalent put your code in a function and use setTimeout() to call it.

eg:

I2C1.setup({ sda: D4, SCL: D5 });

function i2c_do(i2c,addr, w,r){
    i2c.writeTo(addr, w);
    i2c.readFrom(addr,r);
}

setTimeout(function(){i2c_do(I2C1,0x11,0­,2);},1000);