Added Promise support with capabilities test to renderFile

lib/ejs.js

@@ -220,13 +220,32 @@ function handleCache(options, template) {
 
 function tryHandleCache(options, data, cb) {
   var result;
-  try {
-    result = handleCache(options)(data);
+  if (!cb) {
+    if (typeof Promise == 'function') {
+      return new Promise(function (resolve, reject) { // eslint-disable-line no-undef
+        try {
+          result = handleCache(options)(data);
+          resolve(result);
+        }
+        catch (err) {
+          reject(err);
+        }
+      });
+    }
+    else {
+      throw new Error('Please provide a callback function');
+    }
   }
-  catch (err) {
-    return cb(err);
+  else {
+    try {
+      result = handleCache(options)(data);
+    }
+    catch (err) {
+      return cb(err);
+    }
+
+    cb(null, result);
   }
-  return cb(null, result);
 }
 
 /**
@@ -399,17 +418,27 @@ exports.render = function (template, d, o) {
  */
 
 exports.renderFile = function () {
-  var filename = arguments[0];
-  var cb = arguments[arguments.length - 1];
+  var args = Array.prototype.slice.call(arguments);
+  var filename = args.shift();
+  var cb;
   var opts = {filename: filename};
   var data;
 
-  if (arguments.length > 2) {
-    data = arguments[1];
-
-    // No options object -- if there are optiony names
-    // in the data, copy them to options
-    if (arguments.length === 3) {
+  // Do we have a callback?
+  if (typeof arguments[arguments.length - 1] == 'function') {
+    cb = args.pop();
+  }
+  // Do we have data/opts?
+  if (args.length) {
+    // Should always have data obj
+    data = args.shift();
+    // Normal passed opts (data obj + opts obj)
+    if (args.length) {
+      // Use shallowCopy so we don't pollute passed in opts obj with new vals
+      utils.shallowCopy(opts, args.pop());
+    }
+    // Special casing for Express (opts-in-data)
+    else {
       // Express 4
       if (data.settings) {
         if (data.settings.views) {
@@ -424,11 +453,6 @@ exports.renderFile = function () {
         utils.shallowCopyFromList(opts, data, _OPTS_EXPRESS);
       }
     }
-    else {
-      // Use shallowCopy so we don't pollute passed in opts obj with new vals
-      utils.shallowCopy(opts, arguments[2]);
-    }
-
     opts.filename = filename;
   }
   else {