taisp
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+<!doctype html>
+<html lang="en">
+	<head>
+		<title>JavaScript Patterns</title>
+		<meta charset="utf-8">
+	</head>
+	<body>
+		<script>
+			/* Title: Visitor
+			 Description: Represent an operation to be performed on the elements of an object structure.
+			 Visitor lets you define a new operation without changing the classes of the elements on which it operates.
+			 */
+
+			var Employee = function (name, salary, vacation) {
+				var self = this;
+
+				this.accept = function (visitor) {
+					visitor.visit(self);
+				};
+
+				this.getName = function () {
+					return name;
+				};
+
+				this.getSalary = function () {
+					return salary;
+				};
+
+				this.setSalary = function (sal) {
+					salary = sal;
+				};
+
+				this.getVacation = function () {
+					return vacation;
+				};
+
+				this.setVacation = function (vac) {
+					vacation = vac;
+				};
+			};
+
+			var ExtraSalary = function () {
+				this.visit = function (emp) {
+					emp.setSalary(emp.getSalary() * 1.1);
+				};
+			};
+
+			var ExtraVacation = function () {
+				this.visit = function (emp) {
+					emp.setVacation(emp.getVacation() + 2);
+				};
+			};
+
+			// log helper
+			var log = (function() {
+				var log = "";
+
+				return {
+					add: function(msg) { log += msg + "\n"; },
+					show: function() { alert(log); log = ""; }
+				}
+			})();
+
+			//example
+			function run() {
+
+				var employees = [
+					new Employee("John", 10000, 10),
+					new Employee("Mary", 20000, 21),
+					new Employee("Boss", 250000, 51)
+				];
+
+				var visitorSalary = new ExtraSalary();
+				var visitorVacation = new ExtraVacation();
+
+				for (var i = 0, len = employees.length; i < len; i++) {
+					var emp = employees[i];
+
+					emp.accept(visitorSalary);
+					emp.accept(visitorVacation);
+					log.add(emp.getName() + ": $" + emp.getSalary() +
+							" and " + emp.getVacation() + " vacation days");
+				}
+
+				log.show();
+			}
+
+			// reference
+			// http://www.dofactory.com/javascript/visitor-design-pattern
+		</script>
+	</body>
+</html>