General-purpose validator for ngModel. angular.js comes with several built-in validation mechanism for input fields (ngRequired, ngPattern etc.) but using an arbitrary validation function requires creation of a custom formatters and / or parsers. The ng-validate directive makes it easy to use any function(s) defined in scope as a validator funct…

ngValidate.js

/**
 * General-purpose validator for ngModel. angular.js comes with several built-in
 * validation mechanism for input fields (ngRequired, ngPattern etc.) but using
 * an arbitrary validation function requires creation of a custom formatters and /
 * or parsers. The ng-validate directive makes it easy to use any function(s)
 * defined in scope as a validator function(s). A validator function will
 * trigger validation on both model and input changes.
 * 
 * @example <input ng-validate=" 'myValidatorFunction($value)' ">
 * @example <input ng-validate="{ foo : '$value > anotherModel', bar :
 *          'validateFoo($value)' }">
 * @example <input ng-validate="{ foo : '$value > anotherModel' }"
 *          ng-validate-watch=" 'anotherModel' ">
 * @example <input ng-validate="{ foo : '$value > anotherModel', bar :
 *          'validateFoo($value)' }" ng-validate-watch=" { foo : 'anotherModel' } ">
 * 
 * @param ng-validate
 *            {string|object literal} If strings is passed it should be a
 *            scope's function to be used as a validator. If an object literal
 *            is passed a key denotes a validation error key while a value
 *            should be a validator function. In both cases validator function
 *            should take a value to validate as its argument and should return
 *            true/false indicating a validation result.
 */
app.directive('ngValidate', function() {
  "use strict";
	return {
		restrict : 'A',
		require : 'ngModel',
		link : function(scope, elm, attrs, ctrl) {
			var validateFn, watch, validators = {}, validateExpr = scope
					.$eval(attrs.ngValidate);

			if (!validateExpr) {
				return;
			}

			if (angular.isString(validateExpr)) {
				validateExpr = {
					validator : validateExpr
				};
			}

			angular.forEach(validateExpr, function(expression, key) {
				validateFn = function(valueToValidate) {
					var result;
					if (scope.$eval(expression, {
						'$value' : valueToValidate
					})) {
						ctrl.$setValidity(key, true);
						result = valueToValidate;
					} else {
						ctrl.$setValidity(key, false);
						result = undefined;
					}
					return result;
				};
				validators[key] = validateFn;
				ctrl.$formatters.push(validateFn);
				ctrl.$parsers.push(validateFn);
			});

			// Support for ng-validate-watch
			if (attrs.ngValidateWatch) {
				watch = scope.$eval(attrs.ngValidateWatch);
				if (angular.isString(watch)) {
					scope.$watch(watch, function() {
						angular.forEach(validators, function(validatorFn, key) {
							validatorFn(ctrl.$modelValue);
						});
					});
				} else {
					angular.forEach(watch, function(expression, key) {
						scope.$watch(expression, function() {
							validators[key](ctrl.$modelValue);
						});
					});
				}
			}
		}
	};
});