The handler.isExtensible()
method is a trap for the [[IsExtensible]]
object internal method, which is used by operations such as Object.isExtensible()
.
The handler.isExtensible()
method is a trap for the [[IsExtensible]]
object internal method, which is used by operations such as Object.isExtensible()
.
new Proxy(target, { isExtensible(target) { } });
The following parameter is passed to the isExtensible()
method. this
is bound to the handler.
target
The target object.
The isExtensible()
method must return a boolean value.
This trap can intercept these operations:
Or any other operation that invokes the [[IsExtensible]]
internal method.
If the following invariants are violated, the trap throws a TypeError
when invoked.
Object.isExtensible(proxy)
must return the same value as Object.isExtensible(target)
. The following code traps Object.isExtensible()
.
const p = new Proxy( {}, { isExtensible(target) { console.log("called"); return true; }, }, ); console.log(Object.isExtensible(p)); // "called" // true
The following code violates the invariant.
const p = new Proxy( {}, { isExtensible(target) { return false; }, }, ); Object.isExtensible(p); // TypeError is thrown
Specification |
---|
ECMAScript Language Specification # sec-proxy-object-internal-methods-and-internal-slots-isextensible |
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | WebView Android | Deno | Node.js | ||
isExtensible |
49 | 12 | 31 | 36 | 10 | 49 | 31 | 36 | 10 | 5.0 | 49 | 1.0 | 6.0.0 |
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy/Proxy/isExtensible