A large number of JavaScript interview questions, if not most of them, can be answered with an understanding of scoping, how this works, and hoisting.

var value = 2;

test();

function test () {
    console.log(typeof value);
    console.log(value);
    var value = 3;
}

You might be expecting the method to print 'number' first, and 2 afterwards, or maybe 3? Try running it! Why does it print 'undefined' and then undefined? Well, hello hoisting! It'll be easier for you to picture it if I re-arrange the code to how it ends up after hoisting takes place. Let's have a look.

var value;

function test () {
    var value;
    console.log(typeof value);
    console.log(value);
    value = 3;
}

value = 2;

test();

So, that's why: the value declaration at the end of the test function actually got hoisted to the top of the scope, and also the reason why test didn't meet us with a TypeError exception warning us about undefined not being a function. Keep in mind that if we used the variable form of declaring the test function, we would in fact have gotten that error, because although var test would've been hoisted, the assignment wouldn't have been, effectively becoming the following:

var value;
var test;

value = 2;

test();

test = function () {
    var value;
    console.log(typeof value);
    console.log(value);
    value = 3;
};

The above wouldn't work as expected, because test isn't defined by the time we want to invoke it.