JavaScript-Objektakzessor

JavaScript 访问器（Getter 和 Setter）

ECMAScript 5 (2009) 引入了 Getter 和 Setter。

Getter 和 Setter 允许您定义对象访问器（被计算的属性）。

JavaScript Getter（get 关键词）

本例使用 lang 属性来获取 language 属性的值。

Instance

// Create an object:
var person = {
  firstName: "Bill",
  lastName : "Gates",
  language : "en",
  get lang() {
    return this.language;
  }
};
// Use a getter to display data from the object:
document.getElementById("demo").innerHTML = person.lang;

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JavaScript Setter（set 关键词）

本例使用 lang 属性来设置 language 属性的值。

Instance

var person = {
  firstName: "Bill",
  lastName : "Gates",
  language : "",
  set lang(lang) {
    this.language = lang;
  }
};
// Use a setter to set the object property:
person.lang = "en";
// Display data from the object:
document.getElementById("demo").innerHTML = person.language;

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JavaScript 函数还是 Getter？

下面两个例子的区别在哪里？

例子 1

var person = {
  firstName: "Bill",
  lastName : "Gates",
  fullName : function() {
    return this.firstName + " " + this.lastName;
  }
};
// 使用方法来显示来自对象的数据：
document.getElementById("demo").innerHTML = person.fullName();

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例子 2

var person = {
  firstName: "Bill",
  lastName : "Gates",
  get fullName() {
    return this.firstName + " " + this.lastName;
  }
};
// Use a getter to display data from the object:
document.getElementById("demo").innerHTML = person.fullName;

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例子 1 以函数形式访问 fullName：person.fullName()。

例子 2 以属性形式访问 fullName：person.fullName。

第二个例子提供了更简洁的语法。

数据质量

使用 getter 和 setter 时，JavaScript 可以确保更好的数据质量。

In this example, use lang 属性以大写形式返回 language 属性的值：

Instance

// Create an object:
var person = {
  firstName: "Bill",
  lastName : "Gates",
  language : "en",
  get lang() {
    return this.language.toUpperCase();
  }
};
// Use a getter to display data from the object:
document.getElementById("demo").innerHTML = person.lang;

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In this example, use lang The property stores uppercase values in language In properties:

Instance

var person = {
  firstName: "Bill",
  lastName : "Gates",
  language : "",
  set lang(lang) {
    this.language = lang.toUpperCase();
  }
};
// Use a setter to set the object property:
person.lang = "en";
// Display data from the object:
document.getElementById("demo").innerHTML = person.language;

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Why use Getters and Setters?

  • It provides a more concise syntax
  • It allows the syntax of properties and methods to be the same
  • It can ensure better data quality
  • Is conducive to background work

An instance of a counter

Instance

var obj = {
  counter : 0,
  get reset() {
    this.counter = 0;
  },
  get increment() {
    this.counter++;
  },
  get decrement() {
    this.counter--;
  },
  set add(value) {
    this.counter += value;
  },
  set subtract(value) {
    this.counter -= value;
  }
};
// Counter-Operationen:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;
Object.defineProperty()

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Object.defineProperty() Methods can also be used to add Getters and Setters:

Instance

// Definition of the object
var obj = {counter : 0};
// Definition of setters
Object.defineProperty(obj, "reset", {
  get : function () {this.counter = 0;}
});
Object.defineProperty(obj, "increment", {
  get : function () {this.counter++;}
});
Object.defineProperty(obj, "decrement", {
  get : function () {this.counter--;}
});
Object.defineProperty(obj, "add", {
  set : function (value) {this.counter += value;}
});
Object.defineProperty(obj, "subtract", {
  set : function (value) {this.counter -= value;}
});
// Counter-Operationen:
obj.reset;
obj.add = 5;
obj.subtract = 1;
obj.increment;
obj.decrement;

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Browser-Unterstützung

Internet Explorer 8 oder früher unterstützen Getter und Setter nicht:

Ja 9.0 Ja Ja Ja