The benefits of declaring variables at the top of the function body in JavaScript

Question

I am reading Douglas Crockford\'s book \"Javascript: The Good Parts\". He is talking about scope and saying that JS doesn\'t have block scope:

In many mod

Answer 1

Declaring variables at the top helps you avoid situations like this:

function outer() {
  var i = 50;

  function inner() {
    alert(i);
    var i= 30;
  }
  inner();
}

outer();

Many people would expect the alert to show 50, and they would be surprised to see undefined. That's because the i variable is declared within the inner function, but it isn't initialized until after the alert. So it has full function scope, even though it's declared after its initial use.