handler.preventExtensions()
handler.preventExtensions() is a JavaScript method in the Proxy category. Traps Object.preventExtensions. The syntax is preventExtensions(target). A typical example: handler = { preventExtensions(t) { return true } }. A close sibling is Proxy(), which creates a Proxy. A close sibling is handler.get(), which traps property access. A close sibling is handler.set(), which traps property assignment. A close sibling is handler.has(), which traps the in operator. More about this category: Proxy handlers for custom object behavior. Related Proxy methods: Proxy(), handler.get(), handler.set(), handler.has(), handler.construct(), handler.defineProperty(), handler.getOwnPropertyDescriptor(), handler.getPrototypeOf(). This page is part of the free JS Reference documentation covering 1027+ methods, each with syntax, parameters, return values, examples, and common pitfalls. You can try handler.preventExtensions() immediately in the JavaScript playground, look up unfamiliar terms in the glossary, or return to the JS Reference homepage.