const object = {  foo: 42,};console.log(Object.isFrozen(object));// Expected output: falseObject.freeze(object);console.log(Object.isFrozen(object));// Expected output: true

Object.isFrozen(obj)

// A new object is extensible, so it is not frozen.Object.isFrozen({}); // false// An empty object which is not extensible// is vacuously frozen.const vacuouslyFrozen = Object.preventExtensions({});Object.isFrozen(vacuouslyFrozen); // true// A new object with one property is also extensible,// ergo not frozen.const oneProp = { p: 42 };Object.isFrozen(oneProp); // false// Preventing extensions to the object still doesn't// make it frozen, because the property is still// configurable (and writable).Object.preventExtensions(oneProp);Object.isFrozen(oneProp); // false// Deleting that property makes the object vacuously frozen.delete oneProp.p;Object.isFrozen(oneProp); // true// A non-extensible object with a non-writable// but still configurable property is not frozen.const nonWritable = { e: "plep" };Object.preventExtensions(nonWritable);Object.defineProperty(nonWritable, "e", {  writable: false,}); // make non-writableObject.isFrozen(nonWritable); // false// Changing that property to non-configurable// then makes the object frozen.Object.defineProperty(nonWritable, "e", {  configurable: false,}); // make non-configurableObject.isFrozen(nonWritable); // true// A non-extensible object with a non-configurable// but still writable property also isn't frozen.const nonConfigurable = { release: "the kraken!" };Object.preventExtensions(nonConfigurable);Object.defineProperty(nonConfigurable, "release", {  configurable: false,});Object.isFrozen(nonConfigurable); // false// Changing that property to non-writable// then makes the object frozen.Object.defineProperty(nonConfigurable, "release", {  writable: false,});Object.isFrozen(nonConfigurable); // true// A non-extensible object with a configurable// accessor property isn't frozen.const accessor = {  get food() {    return "yum";  },};Object.preventExtensions(accessor);Object.isFrozen(accessor); // false// When we make that property non-configurable it becomes frozen.Object.defineProperty(accessor, "food", {  configurable: false,});Object.isFrozen(accessor); // true// But the easiest way for an object to be frozen// is if Object.freeze has been called on it.const frozen = { 1: 81 };Object.isFrozen(frozen); // falseObject.freeze(frozen);Object.isFrozen(frozen); // true// By definition, a frozen object is non-extensible.Object.isExtensible(frozen); // false// Also by definition, a frozen object is sealed.Object.isSealed(frozen); // true

Object.isFrozen(1);// TypeError: 1 is not an object (ES5 code)Object.isFrozen(1);// true                          (ES2015 code)

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This page was last modified on⁨Jul 20, 2025⁩ byMDN contributors.