if I have an object like
let person = {
firstName: 'Krishna',
lastName: 'Jai',
age: 12
}
person.firstName = 'Kumar';
console.log(person);
//output
Object { firstname: 'Kumar', lastName: 'Jai', age: 12 }
But I should not let any user to change the firstName of person. how to make firstName immutable so that its value cannot be overriden?
If you already have a property in place, you can modify it's descriptor's writable property to false like that:
Object.defineProperty(person, 'firstName', {
writable: false,
configurable: false
});
configurable: false should be specified to prevent future modifications of the firstName property, e.g. changing writable back to true.
Read more here about property descriptors.
If you're defining a property that didn't exist before, then all descriptor properties are defaulted to false and the only things you need to specify are value and enumerable:
Object.defineProperty(person, "firstName", {
value: "Krishna",
enumerable: true
});
firstName open to re-configuring (and therefore becoming writable again): jsfiddle.net/11fcmftdconfigurable: false, it protects it: jsfiddle.net/11fcmftd/1You have a couple of options, but probably the simplest is to make a read-only, non-configurable property:
let person = {
lastName: 'Jai',
age: 12
};
Object.defineProperty(person, "firstName", {
value: "Krishna",
enumerable: true
});
The flags writable and configurable both default to false when, as above, you're defining a new property. (You don't have to make it enumerable, as far as that goes, but...)
Example:
let person = {
lastName: 'Jai',
age: 12
};
Object.defineProperty(person, "firstName", {
value: "Krishna",
enumerable: true
});
console.log("before: ", person.firstName);
person.firstName = "Mohinder";
console.log("after setting in loose mode:", person.firstName);
function foo() {
"use strict";
console.log("trying to set in strict mode:");
person.firstName = "Mohinder"; // Error
}
foo();Or if you want to apply the change after the fact, you need to specify the flags:
let person = {
firstName: "Krishna",
lastName: 'Jai',
age: 12
};
Object.defineProperty(person, "firstName", {
writable: false,
configurable: false
});
Example:
let person = {
firstName: "Krishna",
lastName: 'Jai',
age: 12
};
Object.defineProperty(person, "firstName", {
writable: false,
configurable: false
});
console.log("before: ", person.firstName);
person.firstName = "Mohinder";
console.log("after setting in loose mode:", person.firstName);
function foo() {
"use strict";
console.log("trying to set in strict mode:");
person.firstName = "Mohinder"; // Error
}
foo();
configurable is false, I can still change writable from true to false, which is...just wrong. :-) (But clearly stated in Step 8.a.i in the spec. Bizarre.)You could use a getter method and omit the setter.
let person = {
get firstName() { return 'Krishna'; },
lastName: 'Jai',
age: 12
};
person.firstName = 'Kumar';
console.log(person);
Object.defineProperty(person, "firstName", {get : function(){ return "Nina Scholz"}});console.log(person.firstName)
Stringtype. The right phrase should be read only and non-configurable property.