JavaScript设计模式之策略模式详解

/*
 * pre：策略模式
 * 示例：公司计算奖金，分A、B、C 三种绩效，计算方式如下
 * 绩效为A，奖金乘以系数5
 * 绩效为B，奖金乘以系数4
 * 绩效为C，奖金乘以系数3
 */
//-------- 示例1 ----------
var calculateBonus = function(performanceLevel, salary) {
 if(performanceLevel === 'A') {
  return salary * 5;
 }
 if(performanceLevel === 'B') {
  return salary * 4;
 }
 if(performanceLevel === 'C') {
  return salary * 3;
 }
};
console.log(calculateBonus('A', 2000));
/*
 缺点:1、函数体系庞大，拥有太多的if-else语句；
  2、如果增加绩效D，需修改内部函数，违背封闭-开放原则；
  3、复用性差，其他地方如果用到计算奖金，只能赋值黏贴；
 */
//--------- 示例2 ------------
var performanceA = function(salary) {
 return salary * 5;
};
var performanceB = function(salary) {
 return salary * 4;
};
var performanceC = function(salary) {
 return salary * 3;
};
var calculateBonus = function(performanceLevel, salary) {
 if(performanceLevel === 'A') {
  return performanceA(salary);
 }
 if(performanceLevel === 'B') {
  return performanceB(salary);
 }
 if(performanceLevel === 'C') {
  return performanceC(salary);
 }
};
console.log(calculateBonus('A', 2000)); 
/*
 缺点：1、函数体系庞大，系统变化时缺乏弹性
 */
//--------- 示例3 ------------
// 策略模式重构：定义一系列算法，将它们一个个封装起来。
var performanceA = function(){};
performanceA.prototype.caculate = function(salary){
 return salary * 5;
};
var performanceB = function(){};
performanceB.prototype.caculate = function(salary){
 return salary * 4;
};
var performanceC = function(){};
performanceC.prototype.caculate = function(salary){
 return salary * 3;
};

var Bonus = function(){
 this.salary = null;
 this.strategy = null;
};
Bonus.prototype.setSalary = function(salary){
 this.salary = salary;
};
Bonus.prototype.setStrategy = function(strategy){
 this.strategy = strategy;
}
Bonus.prototype.getBonus = function(){
 return this.strategy.caculate(this.salary);
}

var bonus = new Bonus();
bonus.setSalary(2000);
bonus.setStrategy(new performanceA());
console.log(bonus.getBonus());

// ----------- 示例4 ---------------
// javaScript版本
var Strategies = {
 "A":function(salary){
  return salary * 5;
 },
 "B":function(salary){
  return salary * 4;
 },
 "C":function(salary){
  return salary * 3;
 } 
};
var caculateBonus = function(level,salary){
 return Strategies[level](salary);
};
console.log(caculateBonus("A",2000));