window.onload

window.onload = function() {
  // Some code
};

window.onload = (event) => {
  console.log('page is fully loaded');
};

window.addEventListener('load', (event) => {
  console.log('page is fully loaded');
});

window.onload = function() {
  // Code here
}

//use
window.onload=()=>{};

function load(argument) {
	// body...
}
window.onload = load;

window.onload = function() {
  init();
  doSomethingElse();
};