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Version: 3.28.0

handler.preventExtensions()

The handler.preventExtensions() method is a trap for Object.preventExtensions().

Syntax​

new Proxy(target, {
  preventExtensions(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:

Or any other operation that invokes the [[PreventExtensions]] internal method.

Invariants​

If the following invariants are violated, the trap throws a TypeError when invoked.

  • Object.preventExtensions(proxy) only returns true if Object.isExtensible(proxy) is false.