Hidden Features of JavaScript? [closed]

Answer 1

I'd have to say self-executing functions.

(function() { alert("hi there");})();

Because Javascript doesn't have block scope, you can use a self-executing function if you want to define local variables:

(function() {
  var myvar = 2;
  alert(myvar);
})();

Here, myvar is does not interfere with or pollute the global scope, and disappears when the function terminates.