Javascript Object Data Property Update

Introduction

To change the default property attributes, use the Object.defineProperty() method.

This method accepts three arguments:

  • the object
  • the name of the property
  • a descriptor object.

The properties on the descriptor object match the attribute names:

  • configurable
  • enumerable
  • writable
  • value

You can set one or all of these values to change the corresponding attribute values.

For example: 

let person = {};// www . j a  va  2s  .c  o  m
Object.defineProperty(person, "name", {
    writable: false,
    value: "HTML"
});
console.log(person.name); // "HTML" 
person.name = "Javascript";
console.log(person.name); // "HTML"

This example creates a property called name with a value of "HTML" that is read-only.

The value of this property can't be changed.

Any attempts to assign a new value are ignored in non-strict mode.

In strict mode, an error is thrown when an attempt is made to change the value of a read-only property.

The following code create a non-configurable property. 

let person = {};/*from w  w  w.j  a v a2 s .  com*/
Object.defineProperty(person, "name", {
    configurable: false,
    value: "HTML"
});
console.log(person.name); // "HTML" 
delete person.name;
console.log(person.name); // "HTML"

Here, setting configurable to false means that the property cannot be removed from the object.

Calling delete on the property has no effect in non-strict mode.

It throws an error in strict mode.

Additionally, once a property has been defined as nonconfigurable, it cannot become configurable again.

Any attempt to call Object.defineProperty() and change any attribute other than writable causes an error: 

let person = {};//from  w w w.  j av a 2 s .  c  o  m
Object.defineProperty(person, "name", {
    configurable: false,
    value: "HTML"
});
// Throws an error 
Object.defineProperty(person, "name", {
    configurable: true,
    value: "HTML"
});

When you are using Object.defineProperty(), the values for configurable, enumerable, and writable default to false unless otherwise specified.




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