React.js TypeError: Cannot set property 'innerHTML' of null code example

Example: Cannot set property 'innerHTML' of null

/* Answer to: "Cannot set property 'innerHTML' of null" */

window.onload = function (){
	...
}

/*
  Make sure the <script> tag, containing the javascript is at the
  bottom of the <body> tag.
  
  As long as the <script> tag is below the element it's trying to
  find, the JavaScript should work.
  
  However, if you don't want to be the <script> at the bottom of
  your <body> tag. Wrap your javascript with:
*/