The user enters the URL then clicks the "Go!" button. The onClick event handler calls the function and passes the URL to it.
This example uses a programmer-defined function called webjump. The function is defined in the head section of the page. It has one argument -- the URL of the new Web page to open. (The comment hides the function definition from early Web clients that did not recognize Javascript).
Note that the programmer-defined function calls a built-in function called open. (It calls theopen method of the class window).