Auto execute code in javascript

How to write auto execute javascript code ?

We can achieve it by 2 method.

1- Standard auto execute function.

2- Arrow function.

Standard auto execute function.

<script>
(function() {
  const iamvar1= 'Iam var 1';
  console.log('Auto Execute 1 function');
})();
</script>

Arrow function.

<script>
(()=> {
  const iamvar2= 'Iam var 2';
  console.log('Auto Execute 2 function');
})();

</script>