Question

I would like to know is it possible to save some, for example,simplemath.js file with

function ADD(a, b)
{
   return a + b;
}

simple function, run opera’s or some other browser’s javascript console, include somehow this (simplemath.js) file, call ADD(2, 5), and get a result in console or execute javascript code on current web page and manipulate with it’s content. How can I do that? How can I use javascript functions from external files in web-browser’s javascript console?

// EDITS

simplemath.js is just local file, somewhere on hard drive (c:\temp\simplemath.js), no localhost web servers running. I want to run scripts from it on any web page and get result similar to typing javascript: function ADD(a, b){return a+b;} alert(ADD(1, 41);) in browsers address bar, but via console, and load ADD function from external file.

Answer 1

You can include your simplemath.js file as a userscript into Opera:

If enabled, User JavaScript will be loaded on most pages that you
visit, including pages in any frames and inline frames. Any global
functions and variables created in the User JavaScript will be
available, and can be read by any scripts on these pages. For this
reason, to protect your privacy and security, we recommend that you do
not include any sensitive information in your User JavaScript

You can enable it globally or on specific pages only. Opera does also support greasemonkey scripts, a Firefox addon. Yet (at least in FF) they usually run in a sandbox, so they will not leak global variables into the webpage where it would be accessible from the console (unless you explicitly state so).