var value = null; console.log(_.isNull(value)); // true var value2 = undefined; console.log(_.isNull(value2)); // false var value3 = "hello"; console.log(_.isNull(value3)); // falseIn the above examples, we use _isNull to check if a value is null. It returns true only if the value is exactly null, not undefined or any other non-null value. The _isNull method is part of the underscore package library, which is a utility library for working with arrays, functions, objects, and other common data structures in JavaScript. It provides a wide range of useful methods for working with data in functional programming style.