What is Object.defineProperty() in Javascript?

Object.defineProperty() is a method that allows you to define your own properties on an object. It takes three arguments: the object to modify, the name of the property, and a function to define the property's value.

Here's an example:

let myObj = {};
Object.defineProperty(myObj, "length", {
    value: function() {
    return this.length;
    }
});

This code defines a new property, length, on myObj. The value of the property is a function that returns the length of the object. You can also use Object.defineProperty() to change the value of an existing property:

Object.defineProperty(myObj, "length", {
	value: 10
});

Now the length property on myObj has a value of 10. Object.defineProperty() can also be used to delete properties:

Object.defineProperty(myObj, "length", {
	delete: true
});

Now the length property will be deleted from myObj if it is ever set.