Object.isSealed()

Object.isSealed() 静态方法确定对象是否为 sealed。

¥The Object.isSealed() static method determines if an object is sealed.

语法

¥Syntax

Object.isSealed(obj)

返回值

¥Return value

Boolean 指示给定对象是否被密封。

¥A Boolean indicating whether or not the given object is sealed.

描述

¥Description

如果对象被密封，则返回 true，否则返回 false。如果一个对象不是 extensible 并且它的所有属性都是不可配置的，因此不可移除（但不一定不可写），则该对象被密封。

¥Returns true if the object is sealed, otherwise false. An object is sealed if it is not extensible and if all its properties are non-configurable and therefore not removable (but not necessarily non-writable).

示例

¥Examples

使用 Object.isSealed

¥Using Object.isSealed

// Objects aren't sealed by default.
const empty = {};
Object.isSealed(empty); // false

// If you make an empty object non-extensible,
// it is vacuously sealed.
Object.preventExtensions(empty);
Object.isSealed(empty); // true

// The same is not true of a non-empty object,
// unless its properties are all non-configurable.
const hasProp = { fee: "fie foe fum" };
Object.preventExtensions(hasProp);
Object.isSealed(hasProp); // false

// But make them all non-configurable
// and the object becomes sealed.
Object.defineProperty(hasProp, "fee", {
  configurable: false,
});
Object.isSealed(hasProp); // true

// The easiest way to seal an object, of course,
// is Object.seal.
const sealed = {};
Object.seal(sealed);
Object.isSealed(sealed); // true

// A sealed object is, by definition, non-extensible.
Object.isExtensible(sealed); // false

// A sealed object might be frozen,
// but it doesn't have to be.
Object.isFrozen(sealed); // true
// (all properties also non-writable)

const s2 = Object.seal({ p: 3 });
Object.isFrozen(s2); // false
// ('p' is still writable)

const s3 = Object.seal({
  get p() {
    return 0;
  },
});
Object.isFrozen(s3); // true
// (only configurability matters for accessor properties)

非对象论证

¥Non-object argument

在 ES5 中，如果该方法的参数不是对象（原语），那么它将导致 TypeError。在 ES2015 中，如果传递非对象参数，它将返回 true，不会出现任何错误，因为根据定义，原语是不可变的。

¥In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES2015, it will return true without any errors if a non-object argument is passed, since primitives are, by definition, immutable.

Object.isSealed(1);
// TypeError: 1 is not an object (ES5 code)

Object.isSealed(1);
// true                          (ES2015 code)

规范

Specification
ECMAScript Language Specification # sec-object.issealed

¥Specifications

浏览器兼容性

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¥Browser compatibility

也可以看看

¥See also