What Is an Object Property Descriptor in JavaScript?

Object property descriptors are attributes that describe the configuration of a specific object property. For example, to create an object property "foo" that does not appear in enumeration of object's properties you would set the enumeration descriptor as false like so:

const obj = { bar: 'baz' };
const objDescriptor = { value: 'bar', enumerable: false };

Object.defineProperty(obj, 'foo', objDescriptor);

for (const prop in obj) {
    console.log(prop); // 'bar'
}

Based on the property descriptors, an object property can be concluded as being either a data property or an accessor property. Both data and accessor property descriptors are objects that have the following keys/descriptors in common:

• enumerable — if true, the property will show up during enumeration of the object properties;
• configurable — if false, it prevents deletion of the property as well as any changes to the object property's descriptors.

In addition to those, a data property has the following descriptors:

• value — any value that's associated with the property;
• writable — if true, the property value can be reassigned.

In contrast, an accessor property has the following descriptors in addition to the common ones between the two:

• get — a getter function for the property;
• set — a setter function for the property.

You can use the following methods to specify data and accessor property descriptors:

• Object.create() — used to create a new object (using an existing object as the prototype of the newly created object); it allows specifying data descriptors for each property you add to the object;
• Object.defineProperty() — used to define (or modify) a single object property with option to specify data descriptors;
• Object.defineProperties() — used to define (or modify) multiple object properties with option to specify data descriptors.

You can use the following methods to get details of data and accessor property descriptors:

• Object.getOwnPropertyDescriptor() — returns an object with property descriptors for a specific object property (that's directly present on an object and not in the object's prototype chain);
• Object.getOwnPropertyDescriptors() — returns all own property descriptors for a given object.