Can you give an example of when you really need a semicolon?

It is recommended to use semicolons after every statement in JavaScript. For example, in the below case (that is an IIFE = Immediately Invoked Function Expression) it throws an error ".. is not a function" at runtime due to missing semicolon.

      // define a function
      var fn = (function () {
        //...
      })(
        // semicolon missing at this line

        // then execute some code inside a closure
        function () {
          //...
        }
      )();
      

and it will be interpreted as

      var fn = (function () {
        //...
      })(function () {
        //...
      })();
      

In this case, we are passing the second function as an argument to the first function and then trying to call the result of the first function call as a function. Hence, the second function will fail with a "... is not a function" error at runtime.