simple explanation how to save code that espruino run on start?

The following code seems valid but the led is not blinking. The console output is correct. It is as if digitalWrite is not working.
When I run the code without save() and onInit() functions, inside simple setInterval the led is blinking. Any iade?

var toggle=1;


function start(){
  
setInterval(function() {
  toggle=!toggle;
  digitalWrite(D5, toggle);
  
  console.log(toggle);
}, 1000);

}

function onInit() {
  start();
}