The handler.preventExtensions()
method is a trap for Object.preventExtensions()
.
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Syntax
const p = new Proxy(target, { preventExtensions: function(target) { } });
Parameters
The following parameter is passed to the preventExtensions()
method. this
is bound to the handler.
target
- The target object.
Return value
The preventExtensions()
method must return a boolean value.
Description
The handler.preventExtensions()
method is a trap for Object.preventExtensions()
.
Interceptions
This trap can intercept these operations:
Invariants
If the following invariants are violated, the proxy will throw a TypeError
:
Object.preventExtensions(proxy)
only returnstrue
ifObject.isExtensible(proxy)
isfalse
.
Examples
Trapping of preventExtensions
The following code traps Object.preventExtensions()
.
const p = new Proxy({}, { preventExtensions: function(target) { console.log('called'); Object.preventExtensions(target); return true; } }); console.log(Object.preventExtensions(p)); // "called" // false
The following code violates the invariant.
const p = new Proxy({}, { preventExtensions: function(target) { return true; } }); Object.preventExtensions(p); // TypeError is thrown
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of '[[PreventExtensions]]' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
preventExtensions | Chrome Full support 49 | Edge Full support 12 | Firefox Full support 22 | IE No support No | Opera Full support 36 | Safari Full support 10 | WebView Android Full support 49 | Chrome Android Full support 49 | Firefox Android Full support 22 | Opera Android Full support 36 | Safari iOS Full support 10 | Samsung Internet Android Full support 5.0 | nodejs Full support 6.0.0 |
Legend
- Full support
- Full support
- No support
- No support