add promise helper function

Author: dorkyboi

public/js/filemanager.js

@@ -0,0 +1,22 @@
+/**
+ * Open file manager and return selected files.
+ * Promise is never resolved if window is closed.
+ *
+ * @returns Promise<array> Array of selected files with properties:
+ *      icon        string
+ *      is_file     bool
+ *      is_image    bool
+ *      name        string
+ *      thumb_url   string|null
+ *      time        int
+ *      url         string
+ */
+window.filemanager = function filemanager() {
+    var url = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : '/filemanager';
+    var target = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 'FileManager';
+    var features = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 'width=900,height=600';
+    return new Promise(function (resolve) {
+        window.open(url, target, features);
+        window.SetUrl = resolve;
+    });
+};