title: why source code highlighted in red in debugger chrome devtool
body: <p>Why the code in the source section is all red when i use debugger?
  More over i hover the variable but no information provided about it</p>
  
  <p>see my pic:</p>
  
  <p><a href="https://i.stack.imgur.com/KUww0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KUww0.png" alt="the code in the source section is all red in chrome devtool"></a></p>
  
  <p>I work with react components for a long, but see such behaviour for the first time</p>