当尝试设置属性时,set
语法将对象属性绑定到要调用的函数。
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
{set prop(val) { . . . }}
{set [expression](val) { . . . }}
prop
val
prop
的值的变量的一个别名。在 javascript 中,如果试着改变一个属性的值,那么对应的 setter 将被执行。setter 经常和 getter 连用以创建一个伪属性。不可能在具有真实值的属性上同时拥有一个 setter 器。
使用 set 语法时请注意:
{ set x(v) { }, set x(v) { } }
和 { x: ..., set x(v) { } }
是不允许的 )setter 可以用delete
操作来移除。
这将定义一个对象 language 的伪属性current
,当分配一个值时,将使用该值更新log
:
var language = {
set current(name) {
this.log.push(name);
},
log: []
}
language.current = 'EN';
console.log(language.log); // ['EN']
language.current = 'FA';
console.log(language.log); // ['EN', 'FA']
请注意,current
属性是未定义的,访问它时将会返回 undefined
。
delete
操作符移除一个 setter我们可以使用delete
操作符移除 setter。
delete o.current;
defineProperty
为当前对象定义 setter我们可以随时使用 Object.defineProperty()
给一个已经存在的对象添加一个 setter。
var o = { a:0 };
Object.defineProperty(o, "b", { set: function (x) { this.a = x / 2; } });
o.b = 10; // Runs the setter, which assigns 10 / 2 (5) to the 'a' property
console.log(o.a) // 5
var expr = "foo";
var obj = {
baz: "bar",
set [expr](v) { this.baz = v; }
};
console.log(obj.baz); // "bar"
obj.foo = "baz"; // run the setter
console.log(obj.baz); // "baz"
Specification | Status | Comment |
---|---|---|
ECMAScript 5.1 (ECMA-262) Object Initializer |
Standard | Initial definition. |
ECMAScript 2015 (6th Edition, ECMA-262) Method definitions |
Standard | Added computed property names. |
ECMAScript Latest Draft (ECMA-262) Method definitions |
Draft |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
set | Chrome Full support 1 | Edge Full support Yes | Firefox Full support 2 | IE Full support 9 | Opera Full support 9.5 | Safari Full support 3 | WebView Android Full support 1 | Chrome Android Full support 18 | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes |
Computed property names | Chrome Full support 46 | Edge Full support Yes | Firefox Full support 34 | IE No support No | Opera Full support 47 | Safari No support No | WebView Android Full support 46 | Chrome Android Full support 46 | Edge Mobile Full support Yes | Firefox Android Full support 34 | Opera Android Full support Yes | Safari iOS No support No | Samsung Internet Android Full support 5.0 | nodejs Full support Yes |
delete
Object.defineProperty()
__defineGetter__
__defineSetter__