策略模式

在运行时选择算法。

对外是一个接口，但是根据不同的执行上下文，可以选择某个特定的算法。

var validator = {

  // all available checks
  types: {},

  // error messages in the current 
  // validation session
  messages: [],

  // current validation config
  // name: validation type
  config: {},    

  // the interface method
  // `data` is key => value pairs 
  validate: function (data) {

      var i, msg, type, checker, result_ok;

      // reset all messages
      this.messages = [];

      for (i in data) {

          if (data.hasOwnProperty(i)) {

              type = this.config[i];
              checker = this.types[type];

              if (!type) {
                  continue; // no need to validate
              }
              if (!checker) { // uh-oh
                  throw {
                      name: "ValidationError",
                      message: "No handler to validate type " + type
                  };
              }

              result_ok = checker.validate(data[i]);
              if (!result_ok) {
                  msg = "Invalid value for *" + i + "*, " + checker.instructions;
                  this.messages.push(msg);
              }
          }
      }
      return this.hasErrors();
  },

  // helper
  hasErrors: function () {
      return this.messages.length !== 0;
  }
};

validator.types.isNonEmpty = {
    validate: function (value) {
        return !!value;
    },
    instructions: "the value cannot be empty"
};

validator.types.isNumber = {
    validate: function (value) {
        return !isNaN(Number(value));
    },
    instructions: "the value can only be a valid number, e.g. 1, 3.14 or 2010"
};

validator.types.isAlphaNum = {
    validate: function (value) {
        return !String(value).replace(/[a-z0-9]/ig, "").length;
    },
    instructions: "the value can only contain characters and numbers, no special symbols"
};

validator.config = {
    first_name: 'isNonEmpty',
    age: 'isNumber',
    username: 'isAlphaNum'
};

// example codes
var data = {
    first_name: "Super",
    last_name: "Man",
    age: "unknown",
    username: "o_O"
};
validator.validate(data);
if (validator.hasErrors()) {
    console.log(validator.messages.join("\n"));
}