Which script executes first?

In the questions below, there are two scripts: small.js and big.js.

If we assume that small.js loads much faster compared to big.js -- which script executes first?

<script src="big.js"></script>
<script src="small.js"></script>

What if we add async?

<script async src="big.js"></script>
<script async src="small.js"></script>

What if we switch to defer?

<script defer src="big.js"></script>
<script defer src="small.js"></script>