JS context cannot be escaped

[pstjvn]

Unlike tamperMonkey this tool does not seem to provide means to use the global JS context on the top window (in which it is injected) and thus I see no way to access the globally defined APIs added by the site's creators and those are added explicitly for allowing user scripting via such tools.

Example:
Server sent JS file:

window.someFunction = function() { ... }

Tamperish script

document.onreadystatechange = function(e) { 
  if (document.readyState === 'complete') {
    window.someFunction(); // DOES NOT WORK as the symbol is missing.
  }
}

[pstjvn]

After some digging and remembering the 'good old days' a working solution (although not great IMHO) is to prepare the line(s) of script you want to be able to call in the original host context as text and put it in a script tag in the Body of the document. It would look like this:

(function() {
    function executeInTopContext(str) {
        let s = document.createElement('script');
        s.textContent = str;
        document.body.appendChild(s);
        setTimeout(function() {
            document.body.removeChild(s);
        }, 100);
    }

    executeInTopContext(
        // This will work because the script is executed in the original context of the web site.
        `window.my_custom_website_provided_function(${some_variable_from_tamperish_context});`);

})();

Hope this will help someone.