javascript - 在原型(prototype)继承中创建新对象时如何覆盖函数？

Question

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Answer 1

据我所知，最佳实践是在对象原型(prototype)级别定义写入权限。我从阅读 Addy Osmani 的 JavaScript 设计模式中学到了这项技术，它非常有名并且在线开源:http://addyosmani.com/resources/essentialjsdesignpatterns/book/

请查看下面示例中的 sayPlanet 属性。请记住，您不需要将所有其他属性的“可写”设置为 false，我只是在我的示例代码中这样做来说明这一点。与其他仍然有效的方法相比，这种方法提供了更大的灵 active 和可重用性。在这里，您可能会注意到这是原型(prototype)中的 Object.defineProperties 语法。

var human = {
  name: {
    value: '',
    writable: false //only to illustrate default behavior not needed
  },
  gender: {
    value: '',
    writable: false //only to illustrate default behavior not needed
  },
  planetOfBirth: {
    value: "Earth",
    configurable: false //only to illustrate default behavior not needed
  }

};

//here we define function properties at prototype level

Object.defineProperty(human, 'sayGender', {
  value: function() {
    alert(this.name + ' says my gender is ' + this.gender);
  },
  writable: false
});

Object.defineProperty(human, 'sayPlanet', {
  value: function() {
    alert(this.name + ' was born on ' + this.planetOfBirth);
  },
  writable: true
});

//end definition of function properties

var male = Object.create(human, {
  gender: {
    value: 'Male'
  }
});

var female = Object.create(human, {
  gender: {
    value: 'Female'
  }
});

var david = Object.create(male, {
  name: {
    value: 'David'
  },
  planetOfBirth: {
    value: 'Mars'
  }
});

var jane = Object.create(female, {
  name: {
    value: 'Jane'
  }
});

//define the writable sayPlanet function for Jane
jane.sayPlanet = function() {
  alert("something different");
};

//test cases

//call say gender before attempting to ovverride
david.sayGender(); // David says my gender is Male

//attempt to override the sayGender function for david 
david.sayGender = function() {
  alert("I overrode me!")
};
//I tried and failed to change an unwritable fucntion
david.sayGender(); //David maintains that my gender is Male

david.sayPlanet(); // David was born on Mars

jane.sayGender(); // Jane says my gender is Female
jane.sayPlanet(); // something different