There is actually a way to do exactly what the OP asked for. Just render and call the anonymous function like this:

render () { return ( 
 {(() => { if (someCase) { return ( 
someCase
 ) } else if (otherCase) { return ( 
otherCase
 ) } else { return ( 
catch all
 ) } })()} 
 ) }

Not exactly the same, but there is a workaround. There is a section about conditional rendering in theReact documentationthat you should take a look at. The following is an example of what you can do using inline if-else.

render() { const isLoggedIn = this.state.isLoggedIn; return ( 
 {isLoggedIn ? (  ) : (  )} 
 ); }

You can also handle it inside the render function, but before returning jsx.

if (isLoggedIn) { button = ; } else { button = ; } return ( 
  {button} 
 );

Also worth mentioning is what ZekeDroid brought up in the comments. If you are just checking a condition and don't want to render a specific piece of code that doesn't meet the condition, you can use the&& operator.

return ( 
 
Hello!
 {unreadMessages.length > 0 && 
 You have {unreadMessages.length} unread messages. 
 } 
 );