feat(forms): add support for validations

modules/angular2/src/forms/validators.js

@@ -0,0 +1,31 @@
+import {isBlank, isPresent} from 'angular2/src/facade/lang';
+import {List, ListWrapper, StringMapWrapper} from 'angular2/src/facade/collection';
+
+import {ControlGroup, Control} from 'angular2/forms';
+
+export function required(c:Control) {
+  return isBlank(c.value) || c.value === "" ? {"required" : true} : null;
+}
+
+export function nullValidator(c:Control) {
+  return null;
+}
+
+export function compose(validators:List<Function>):Function {
+  return function(c:Control) {
+    return ListWrapper.reduce(validators, (res, validator) => {
+      var errors = validator(c);
+      return isPresent(errors) ? StringMapWrapper.merge(res, errors) : res;
+    }, {});
+  }
+}
+
+export function controlGroupValidator(c:ControlGroup) {
+  var res = {};
+  StringMapWrapper.forEach(c.controls, (control, name) => {
+    if (isPresent(control.errors)) {
+      res[name] = control.errors;
+    }
+  });
+  return StringMapWrapper.isEmpty(res) ? null : res;
+}