Object.isFrozen()
Object.isFrozen()
静态方法确定对象是否冻结。
试一试
语法
js
Object.isFrozen(obj)
参数
obj
-
应检查的对象。
返回值
一个Boolean
,指示给定对象是否已冻结。
描述
当且仅当对象不可扩展、其所有属性都是不可配置的,并且其所有数据属性(即,不是具有 getter 或 setter 组件的访问器属性的属性)都是不可写的时,该对象才被冻结。
示例
使用 Object.isFrozen
js
// A new object is extensible, so it is not frozen.
Object.isFrozen({}); // false
// An empty object which is not extensible
// is vacuously frozen.
const vacuouslyFrozen = Object.preventExtensions({});
Object.isFrozen(vacuouslyFrozen); // true
// A new object with one property is also extensible,
// ergo not frozen.
const oneProp = { p: 42 };
Object.isFrozen(oneProp); // false
// Preventing extensions to the object still doesn't
// make it frozen, because the property is still
// configurable (and writable).
Object.preventExtensions(oneProp);
Object.isFrozen(oneProp); // false
// Deleting that property makes the object vacuously frozen.
delete oneProp.p;
Object.isFrozen(oneProp); // true
// A non-extensible object with a non-writable
// but still configurable property is not frozen.
const nonWritable = { e: "plep" };
Object.preventExtensions(nonWritable);
Object.defineProperty(nonWritable, "e", {
writable: false,
}); // make non-writable
Object.isFrozen(nonWritable); // false
// Changing that property to non-configurable
// then makes the object frozen.
Object.defineProperty(nonWritable, "e", {
configurable: false,
}); // make non-configurable
Object.isFrozen(nonWritable); // true
// A non-extensible object with a non-configurable
// but still writable property also isn't frozen.
const nonConfigurable = { release: "the kraken!" };
Object.preventExtensions(nonConfigurable);
Object.defineProperty(nonConfigurable, "release", {
configurable: false,
});
Object.isFrozen(nonConfigurable); // false
// Changing that property to non-writable
// then makes the object frozen.
Object.defineProperty(nonConfigurable, "release", {
writable: false,
});
Object.isFrozen(nonConfigurable); // true
// A non-extensible object with a configurable
// accessor property isn't frozen.
const accessor = {
get food() {
return "yum";
},
};
Object.preventExtensions(accessor);
Object.isFrozen(accessor); // false
// When we make that property non-configurable it becomes frozen.
Object.defineProperty(accessor, "food", {
configurable: false,
});
Object.isFrozen(accessor); // true
// But the easiest way for an object to be frozen
// is if Object.freeze has been called on it.
const frozen = { 1: 81 };
Object.isFrozen(frozen); // false
Object.freeze(frozen);
Object.isFrozen(frozen); // true
// By definition, a frozen object is non-extensible.
Object.isExtensible(frozen); // false
// Also by definition, a frozen object is sealed.
Object.isSealed(frozen); // true
非对象参数
在 ES5 中,如果此方法的参数不是对象(原始值),则会导致TypeError
。在 ES2015 中,如果传递非对象参数,则会返回 true
且不会出现任何错误,因为原始值在定义上是不可变的。
js
Object.isFrozen(1);
// TypeError: 1 is not an object (ES5 code)
Object.isFrozen(1);
// true (ES2015 code)
规范
规范 |
---|
ECMAScript 语言规范 # sec-object.isfrozen |
浏览器兼容性
BCD 表格仅在启用 JavaScript 的浏览器中加载。