In the previous posts, I discussed about two levels of object protection: Object.preventExtensions and Object.seal. The last level of protection is Object.freeze, which also makes all the properties unchangeable. You cannot add a new property, you cannot delete an existing property, you cannot reconfigure it, and you cannot change its value.
The following code snippet demonstrates the effects of Object.freeze:
let myObj = {
name: "Ali",
};
Object.freeze(myObj);
console.log(Object.isFrozen(myObj)); // true
// You cannot add new properties. This fails silently.
myObj.age = 19;
console.log(myObj.age); // undefined
// You cannot reconfigure existing properties.
try {
Object.defineProperty(myObj, "name", {
get() {
return "Susan";
},
});
console.log(myObj.name);
} catch (e) {
console.log(e); // TypeError: Cannot redefine property: name
}
// You cannot change property values.
myObj.name = "Susan";
console.log(myObj.name); // Ali
try {
Object.defineProperty(myObj, "name", {
value: "Aria",
});
console.log(myObj.name); // Ali
} catch(e) {
console.log(e); // TypeError: Cannot redefine property: name
}
// You can add new properties to the prototype.
myObj.__proto__.age = 14;
console.log(myObj.age); // 14
// You cannot change the prototype.
try {
Object.setPrototypeOf(myObj, {
grade: 9,
});
console.log(myObj.grade);
} catch (e) {
console.log(e); // TypeError: #<Object> is not extensible
}
try {
myObj.__proto__ = {
grade: 9,
};
console.log(myObj.grade);
} catch (e) {
console.log(e); // TypeError: #<Object> is not extensible
}
In short, Object.freeze prevents extensions to the object and makes all the existing properties non-configurable, and also prevents the values of the existing properties from being changed. In this way, the object becomes immutable.
Related Posts
- JavaScript Basics: Object.create
- JavaScript Basics: Object.assign
- JavaScript Basics: Object.getPrototypeOf and Object.setPrototypeOf
- JavaScript Basics: Object.keys, Object.values, and Object.entries
- JavaScript Basics: Object.is
- JavaScript Basics: Object.prototype.hasOwnProperty
- JavaScript Basics: Object.preventExtensions and Object.isExtensible
- JavaScript Basics: Object.seal and Object.isSealed
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I don't actually think it's a lot of people. I think it's a vocal minority. And it turns out that the most vocal, such as Mattias and Elliott, don't actually understand classes, inheritance or composition nearly as well as they think they do here is last prog which i tried.
class Person {}// A student IS-A person; inheritance seems reasonable class Student extends Person {}// An employee IS-A person; inheritance seems reasonable class Employee extends Person {}// Oops. What if someone is *both* a student and an employee?~// If we're in a language that allows only single inheritance, then we're just sunk// And even if we're in a language that allows multiple inheritance,// we may run into ambiguity issues since we've inherited Person twice
class StudentEmployee extends Student, Employee {} ???` @ghasemkiani
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