Check out example codes for "script tag in html". It will help you in understanding the concepts better.

Code Example 1

/*
There is no actual way to put javascript inside an HTML attribute
But there are some event attribute that can trigger JavaScript 
functions.
Otherwise you have to use <script> tag or external JavaScript
*/

Code Example 2

<script>
  //Insert JS scripts here
  var html
  html = "You can use the <script> tag to incorporate JS code into your HTML code"
  console.log(html)
</script>

Code Example 3

<script>
	//JavaScript here
</script>

Code Example 4

<script>
  // Write JS here
</script>

<script src="link/to/js/file.js"></script>

Learn ReactJs, React Native from akashmittal.com