What is the use of isNaN function? with code example

 Here are examples of each:

1. Using an expression:

javascript
const greet = function() {
  console.log('Hello, world!');
};

greet(); // calling the function using an expression

In this example, we defined a function expression named greet. We then called the function by using the function name followed by parentheses ().

2. Using the function name:

javascript
function greet() {
  console.log('Hello, world!');
}

greet(); // calling the function using the function name

In this example, we defined a function named greet. We then called the function by using the function name followed by parentheses ().

3. Using an arrow function:

javascript
const greet = () => {
  console.log('Hello, world!');
};

greet(); // calling the function using an arrow function

In this example, we defined an arrow function named greet. We then called the function by using the function name followed by parentheses ().

Note that all three methods of calling a function require that the function be defined first. Once the function is defined, you can call it using any of the above methods.