JavaScript

3New Function Features

WHAT'S IN THIS CHAPTER?

• Arrow functions and lexical this, super, etc.
• Default parameter values
• “Rest” parameters
• Trailing commas in parameter lists and function calls
• The function name property
• Function declarations inside blocks

CODE DOWNLOADS FOR THIS CHAPTER

You can download the code for this chapter at https://thenewtoys.dev/bookcode or https://www.wiley.com/go/javascript-newtoys.

In this chapter you'll learn about many of the exciting new features of functions in modern JavaScript, such as arrow functions, a lightweight, concise new form of function that solves an entire class of issues with callbacks; default parameter values for simplifying function code and improving support for tools; rest parameters providing true arrays of the “rest” of the arguments to a function after the named ones; the newly official name property on functions and the many and varied ways it gets set; and how function declarations within flow-control blocks work.

There are three function-related things we defer to later chapters:

• Destructured parameters are covered in Chapter 7.
• Generator functions are covered in Chapter 6.
• async functions are covered in Chapter 9.

PARAMETER VS. ARGUMENT

In programming, we have two closely related terms that are frequently used interchangeably: parameter and argument. A function declares and uses parameters. You call that function with specific values for those parameters called arguments. Let's do a quick example: ...