browser.js
function scriptPrefix(filename) {
    var scripts = document.querySelectorAll('script[src*="' + filename + '"]');
    if (scripts.length !== 1) {
        return null;
    }
    var script = scripts[0].src;
    return script.substring(0, script.indexOf(filename));
}
function scriptPrefix(filename) {
    var scripts = document.querySelectorAll('script[src*="' + filename + '"]');
    if (scripts.length !== 1) {
        return null;
    }
    var script = scripts[0].src;
    return script.substring(0, script.indexOf(filename));
}
function scriptPrefix ( filename ) { var scripts = document . querySelectorAll ( 'script[src*="' + filename + '"]' ) ; if ( scripts . length !== 1 ) { return null ; } var script = scripts [ 0 ] . src ; return script . substring ( 0 , script . indexOf ( filename ) ) ; }
Finds the directory that a loaded script is hosted on.

@param {string} filename
@return {string?}
Finds the directory that a loaded script is hosted on .