I'd just like to confirm… declaring (without assigning) variables that have already been declared does absolutely nothing, correct?

Question

My tests suggest that the title is, indeed, correct. But I don't know if there is some subtle nuance that I'm not thinking of. See also: Is there anything wrong with declaring your vars inside of a for loop or an if block?

Answer 1

If they are in the same scope, your test is right. Redeclaring the same variable in the same scope does nothing.

But, if they are not in the same scope, re-declaring a variable in a local scope will create a new variable that will override the original within that scope.

So, this works fine:

var value = "foo";
var value;
console.log(value);   // "foo"

But, this creates a new variable in the local scope that does not have the value of the globally defined one:

var value = "foo";

function test() {
    var value;            // this creates a new variable that is separate
                          // from the globally declared one with the same name
    console.log(value);   // undefined
}

test();