handler.preventExtensions()
method is a trap for
Object.preventExtensions()
.
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const p = new Proxy(target, {
preventExtensions: function(target) {
}
});
The following parameter is passed to the
preventExtensions()
方法。
this
is bound to the handler.
target
The target object.
preventExtensions()
method must return a boolean value.
handler.preventExtensions()
method is a trap for
Object.preventExtensions()
.
This trap can intercept these operations:
If the following invariants are violated, the proxy will throw a
TypeError
:
Object.preventExtensions(
proxy
)
only returns
true
if
Object.isExtensible(
proxy
)
is
false
.
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
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of '[[PreventExtensions]]' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
preventExtensions
|
Chrome 49 | Edge 12 | Firefox 22 | IE No | Opera 36 | Safari 10 | WebView Android 49 | Chrome Android 49 | Firefox Android 22 | Opera Android 36 | Safari iOS 10 | Samsung Internet Android 5.0 | nodejs 6.0.0 |
完整支持
不支持