Added enhanced toFormData implementation with additional options support; (#4704)

Updated default notation for arrays and objects to bracket style;
Added `multer/express.js` tests;
Updated README.md;

Co-authored-by: Jay <jasonsaayman@gmail.com>

lib/utils.js

@@ -366,29 +366,32 @@ function inherits(constructor, superConstructor, props, descriptors) {
  * Resolve object with deep prototype chain to a flat object
  * @param {Object} sourceObj source object
  * @param {Object} [destObj]
- * @param {Function} [filter]
+ * @param {Function|Boolean} [filter]
+ * @param {Function} [propFilter]
  * @returns {Object}
  */
 
-function toFlatObject(sourceObj, destObj, filter) {
+function toFlatObject(sourceObj, destObj, filter, propFilter) {
   var props;
   var i;
   var prop;
   var merged = {};
 
   destObj = destObj || {};
+  // eslint-disable-next-line no-eq-null,eqeqeq
+  if (sourceObj == null) return destObj;
 
   do {
     props = Object.getOwnPropertyNames(sourceObj);
     i = props.length;
     while (i-- > 0) {
       prop = props[i];
-      if (!merged[prop]) {
+      if ((!propFilter || propFilter(prop, sourceObj, destObj)) && !merged[prop]) {
         destObj[prop] = sourceObj[prop];
         merged[prop] = true;
       }
     }
-    sourceObj = Object.getPrototypeOf(sourceObj);
+    sourceObj = filter !== false && Object.getPrototypeOf(sourceObj);
   } while (sourceObj && (!filter || filter(sourceObj, destObj)) && sourceObj !== Object.prototype);
 
   return destObj;
@@ -413,14 +416,15 @@ function endsWith(str, searchString, position) {
 
 
 /**
- * Returns new array from array like object
+ * Returns new array from array like object or null if failed
  * @param {*} [thing]
- * @returns {Array}
+ * @returns {?Array}
  */
 function toArray(thing) {
   if (!thing) return null;
+  if (isArray(thing)) return thing;
   var i = thing.length;
-  if (isUndefined(i)) return null;
+  if (!isNumber(i)) return null;
   var arr = new Array(i);
   while (i-- > 0) {
     arr[i] = thing[i];