javascript - "______ is not defined"异常，不知道为什么

Question

我收到“工作日未定义”错误输出，不知道为什么。非常感谢任何帮助!

(function(exports) {

  var days = ["monday", "tuesday", "wednesday", "thursday"];

  exports.name = function(number) {
    return days[number];

  };
  exports.day = function(name) {

    return days.indexOf(name);

  };

})(this.weekday = {});

console.log(weekday.name(1));

Answer 1

您的代码可能类似于:

var scopeMaster = function() {};

scopeMaster.prototype.testMethod = function() {

  (function(exports) {

    var days = ["monday", "tuesday", "wednesday", "thursday"];

    exports.name = function(number) {
      return days[number];

    };
    exports.day = function(name) {

      return days.indexOf(name);

    };

  })(this.weekday = {});

  console.log(weekday.name(1));

};

scopeMaster.prototype.testMethod();

它说“未定义工作日”，因为工作日搜索局部变量或父范围中的变量。不搜索当前作用域对象中的成员，因此它不会匹配 this.weekday。

您可以通过两种方式做到这一点:

1) 通过声明本地或父作用域变量:

var scopeMaster = function() {};

var weekday = null; // here's the global one

scopeMaster.prototype.testMethod = function() {

  // var weekday = null; // if you want a private local one
  
  (function(exports) {

    var days = ["monday", "tuesday", "wednesday", "thursday"];

    exports.name = function(number) {
      return days[number];

    };
    exports.day = function(name) {

      return days.indexOf(name);

    };

  })(weekday = {});

  console.log(weekday.name(1));

};

scopeMaster.prototype.testMethod();

2) 通过使用当前作用域成员变量:

var scopeMaster = function() {};

scopeMaster.prototype.testMethod = function() {
 
  (function(exports) {

    var days = ["monday", "tuesday", "wednesday", "thursday"];

    exports.name = function(number) {
      return days[number];

    };
    exports.day = function(name) {

      return days.indexOf(name);

    };

  })(this.weekday = {});

  console.log(this.weekday.name(1));

};

scopeMaster.prototype.testMethod();