Object preventExtension vs seal vs freeze

#javascript #preventextensions #seal #freeze

ECMAScript 5 introduced new Object methods to Javascript. Among them preventExtensions, seal, freeze methods will be compared to each other.

`preventExtensions`

An object called by this method can't have any new properties being added.

Example

let person = {
  name: "Agustin",
  age: 27,
};
Object.preventExtensions(person);
Object.isExtensible(person); // return false
person.surname = "Ramirez";
console.log(person.surname); // return undefined
person.name = "Maria";
console.log(person); // return { name: "Maria", age: 27 }
delete person.age;
console.log(person); // return { name: "Maria" }

`seal`

An object called by this method can not have any new properties being added or current properties deleted.

Example

let person = {
  name: "Agustin",
  age: 27,
};
Object.seal(person);
Object.isSealed(person); // return true
// In strict mode this will throw a `TypeError`
person.foo = "something";
console.log(person.foo); // return undefined
person.name = "Maria";
console.log(person); // return { name: "Maria", age: 27 }
delete person.age;
console.log(person); // return { name: "Maria", age: 27 }
Object.defineProperty(person, "name", {
  get: () => "Juan",
}); // Throw TypeError
console.log(person); // return { name: "Maria", age: 27 }

`freeze`

An object called by this method can not have any further changes done to it.

Example

let person = {
  name: "Agustin",
  age: 27,
};
Object.freeze(person);
Object.isFrozen(person); // return true
person.name = "Maria";
console.log(person); // return { name: "Agustin", age: 27 }

shallow only

All of these methods only work on object properties shallowly, meaning that just work with the direct property references.

let person = {
  name: "Agustin", // Prevented, Sealed and Frozen
  age: 27, // Prevented, Sealed and Frozen
  address: {
    // Un-prevented, un-sealed and un-frozen
    country: "Argentina", // Un-prevented, un-sealed and un-frozen
    city: "Corrientes", // Un-prevented, un-sealed and un-frozen
  },
};