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
},
};
Feature matrix
| Feature | default | preventExtensions | seal | freeze |
|---|---|---|---|---|
| add new properties | ✓ | |||
| remove existing properties | ✓ | ✓ | ||
| change existing property values | ✓ | ✓ | ✓ |
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