Test driving the useEffect hook

The effect callback is defined in the useEffect hook's first input argument:

function Title() {
  useEffect(() => {
    window.title = "" 
  })  
}

The most common way of using the create function can be defined by using the JavaScript ES6 syntax with an inline function, (() => {}). For readers interested in learning more about JavaScript ES6, please see the Embracing JavaScript ES6 section in Chapter 10, Building a Website with React.

One of the interesting facts about this effect function is that, thanks to JavaScript closures, it can access all of the variables defined in the functional component:

function Title({ text }) {
  const a = 2
  useEffect(() => {
     console.log(a)
     console.log(text)
  })
}

The create callback function in the preceding code references both the a variable...