Object.preventExtensions()
Object.preventExtensions() is a JavaScript method in the Object category. Prevents new properties from being added. The syntax is Object.preventExtensions(obj). A typical example: Object.preventExtensions({x:1}). A close sibling is Object.keys(), which returns an array of a given object's own enumerable property names. A close sibling is Object.values(), which returns an array of a given object's own enumerable property values. A close sibling is Object.entries(), which returns an array of key/value pairs. A close sibling is Object.assign(), which copies properties from source objects to a target. More about this category: Object methods for object manipulation — keys, values, assign, and more. Related Object methods: Object.keys(), Object.values(), Object.entries(), Object.assign(), Object.create(), Object.defineProperty(), Object.defineProperties(), Object.freeze(). 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 Object.preventExtensions() immediately in the JavaScript playground, look up unfamiliar terms in the glossary, or return to the JS Reference homepage.