var strategies = {
 "S": function(salary) {
  return salary * 4;
 },
 "A": function(salary) {
  return salary * 3;
 },
 "B": function(salary) {
  return salary * 2;
 }
};

// 接收请求
var calculateBonus = function(level, salary) {
 return strategies[level](salary);
};

// 测试
console.log(calculateBonus("S", 20000));
console.log(calculateBonus("A", 20000));
console.log(calculateBonus("B", 20000));

/* 校验策略对象 */
var validateStrategies = {
 isEmpty: function (val, errorMsg) {
  if (!val) {
   return errorMsg;
  }
 },
 isURL: function (val, errorMsg) {
  if (!new RegExp("^(http:\\/\\/|https:\\/\\/)").test(val)) {
   return errorMsg;
  }
 },
 isEmail: function (val, errorMsg) {
  if (!new RegExp('\\w+((-\\w+)|(\\.\\w+))*\\@[A-Za-z0-9]+((\\.|-)[A-Za-z0-9]+)*\\.[A-Za-z0-9]+').test(val)) {
   return errorMsg;
  }
 },
 isMaxLength: function (val, length, errorMsg) {
  if (val.length > length) {
   return errorMsg;
  }
 },
 isMinLength: function (val, length, errorMsg) {
  if (val.length < length) {
   return errorMsg;
  }
 }
};

/* validator类 */
var validator = function () {
 // 缓存验证策略
 this.cache = [];
};

/**
 * 添加要验证的策略
 * @param dom  要验证的dom元素
 * @param rules  验证规则
 */
validator.prototype.add = function (dom, rules) {
 var self = this;
 for (var i = 0, rule; rule = rules[i++];) {
  (function (rule) {
   var strategyAry = rule.strategy.split(":");  // ["isMaxLength", "10"]
   var errorMsg = rule.errorMsg;     // "内容长度不能超过10"
   self.cache.push(function () {
    var strategy = strategyAry.shift();   // "isMaxLength"
    strategyAry.unshift(dom.value);    // ["1@qq", "10"]
    strategyAry.push(errorMsg);     // ["1@qq", "10", "内容长度不能超过10"]
    return validateStrategies[strategy].apply(dom, strategyAry);
   });
  })(rule);
 }
};

/* 开始校验 */
validator.prototype.start = function () {
 for (var i = 0, validateFunc; validateFunc = this.cache[i++];) {
  var errorMsg = validateFunc();
  if (errorMsg) {
   return errorMsg;
  }
 }
};


// 测试

<label for="email">邮箱：</label><input type="text" name="email" value="1@qq">

var validatorInstance = new validator();
validatorInstance.add(
 document.getElementsByName("email")[0], 
 [{
  strategy: "isEmpty",
  errorMsg: "内容不能为空"
 },{
  strategy: "isMaxLength:10",
  errorMsg: "内容长度不能超过10"
 },{
  strategy: "isEmail",
  errorMsg: "email格式不对"
 }]);
errorMsg = validatorInstance.start();