A function is a reusable block of code that groups together a sequence of statements to perform a specific task.

A function declaration :

A parameter is a named variable inside a function’s block which will be assigned the value of the argument passed in when the function is invoked:

To call a function in your code:

ES6 introduces new ways of handling arbitrary parameters through default parameters which allow us to assign a default value to a parameter in case no argument is passed into the function.

To return a value from a function, we use a return statement.

To define a function using function expressions:

To define a function using arrow function notation:

Function definition can be made concise using concise arrow notation:

It’s good to be aware of the differences between function expressions, arrow functions, and function declarations. As you program more in JavaScript, you’ll see a wide variety of how these function types are used.