JavaScript Optional Chaining: Accessing Nested Properties Safely

This is a conditional chaining expression in JavaScript, also known as optional chaining. It is used to access properties of an object without throwing an error if the object or any of its nested properties are null or undefined.

In this expression, it is checking if the object 'this' has a property 'resData', and if it does, then it checks if 'resData' has a nested property 'data'. If both properties exist, the value of 'data' is returned. If any of the properties are null or undefined, the expression returns undefined without throwing an error.