Filter down array of subsite URL's and return the ones that have the specified list.

Filter URL's and Collect List GUIDs

/*
* Part 2.
* Filter down array of subsite URL's and return the ones that have the specified list.
* @param is an array of strings, each of which is a subsite URL.
*/

function GetListGuidsForSubsites(sites) {
    var targetSites = [];
    var siteIndex = 0;

    function controller() {
        if (siteIndex < sites.length) {
            getListGuid(sites[siteIndex]);
        } else if (targetSites.length > 0) {
            console.log('Done collecting list guids.');
            return GetListAndFormData(targetSites);
        }
    }
    controller();

    function createTargetFiles(siteURL) {
        var arr = [];

        for (var i = 0; i < sourceFiles.length; i++) {
            arr.push({ filePath: siteURL + '/Lists/' + listName + '/' + sourceFiles[i].title + '.aspx', title: sourceFiles[i].title });
        }
        return arr;
    }

    function getListGuid(siteURL) {
        var currentcontext = new SP.ClientContext(siteURL);
        var list = currentcontext.get_web().get_lists().getByTitle(listName);
        currentcontext.load(list, 'Id');
        currentcontext.executeQueryAsync(
            function() {
                var listGuid = list.get_id().toString();
                console.log('List found at ' + siteURL);

                targetSites.push({
                    subsiteURL: siteURL,
                    listGUID: listGuid,
                    listName: listName,
                    targetForms: createTargetFiles(siteURL)
                });
                siteIndex++
                return controller();
            },
            function (sender, args) {
                cosole.warn(args.get_message());
                siteIndex++
                return controller();
            });
    }
}