How does “scope” work with multiple script tags for Javascript in an HTML document?

Question

I\'m not quite sure what goes on between

Answer 1

The upper script is executed first in the first example, so it doesn't know about T yet, hence the error.

In the second example, T is well defined and known anywhere as soon as the script tag is executed. This is due to function declarations being hoisted to the top, no matter what the order is, they are always available. Function declaration hoisting is more deeply explained here

The second example after hoisting is applied:

var v,
   T = function(){}; /* using comma like this is short-hand for: var v; var T = function(){}; */

T.prototype.test = function() {
        document.write("a");
    };

v = new T();
v.test();