javaScript策略模式实现表单验证学习

策略模式定义：定义一系列的算法，把它们一个个封装起来，并且使它们可以互相替换。

用策略模式实现表单验证：

    var rules = {
      isNonEmpty: function(value, errorMsg) {
        if (value === '') {
          return errorMsg;
        }
      },
      minLength: function(value, length, errorMsg) {
        if (value.length < length) {
          return errorMsg;
        }
      }
    };

    var Validator = function() {
      this.cache = [];
    }

    Validator.prototype.add = function (dom, rule, errorMsg) {
      var ary = rule.split(':');
      this.cache.push(function() {
        var strategy = ary.shift();
        ary.unshift(dom);
        ary.push(errorMsg);
        return rules[strategy].apply(dom, ary);
      });
    }

    Validator.prototype.start = function() {
      for (var i = 0, validatorFunc; validatorFunc = this.cache[i++];) {
        var msg = validatorFunc();
        if (msg) {
          return msg;
        }
      }
    }

    var validatorFunc = function() {
      var validator = new Validator();

      validator.add(registerForm.username.value, 'isNonEmpty', '用户名不能为空!');
      validator.add(registerForm.password.value, 'minLength:10', '密码不能少于10位!');

      var errorMsg = validator.start();
      return errorMsg;
    }

    var registerForm = document.getElementById('form');

    registerForm.onsubmit = function() {
      var errorMsg = validatorFunc();
      if (errorMsg) {
        alert(errorMsg);
        return false;
      }
    }

使用策略模式让表单验证易于切换、易于理解、易于扩展。