Abel Sanchez and John R. Williams


  • Why do we care?
  • Functions Basics
  • Functions are objects
  • Functions Provide Scope
  • Value and Reference
  • Exercises

Why do we care?

  • We want to bring together data and functionaly into units that make sense to us.
  • We want to want minimize complexity by creating layers of abstraction and hiding the details.
  • We want to organize and share our work.
  • Using objects and functions we can also extend the language. We can create our own types and methods.

How does reverse work?

Do we care?

Functions Basics

Components of a Function

A function is composed of four parts:

  • The keyword function
  • The function name
  • The function parameters
  • The function body

Function Expression

There are two types of functions:

  • Expressions
  • Statements

Function Statement

A function statement is short-hand for a function expression

Expression vs Statement - Simple Rule

If the first token is function, you have a function statement

Your Turn ...

Video: Function Basics

Functions are objects

Functions Are Objects I

Functions are collections of name/value pairs. Just like objects, functions can be:

  • Assigned to a variable
  • Assigned to an object
  • Passed as arguments to a function
  • Returned from a function
  • Can have methods and properties
  • Can be created dynamically

Functions Are Objects II

Assigning a function to a variable.

Your Turn ...

Your Turn ...

Video: Functions Are Objects

Functions Provide Scope

Functions Provide Scope

Any variable declaration with a var inside the function is invisible outside the function.

Scope within a Function

NOTE: child functions have access to parent functions variables and parameters


Your Turn ...

In the following exercise, your task is to output two different messages by adding one keyword.

Your Turn ...

Video: Functions Provide Scope

Value and Reference

Video: Value and reference

Primitive Value Types

Passing Primitive to Function

Function calls also pass primitive types by value.

Your Turn ...

Objects are Passed by Reference

Objects are never copied.

Object Inspection

Objects are never copied.

Your Turn ...

Within the Object

Primitive and object behavior holds.

Keeping the Object Reference

You can keep an object reference even while you reassign the variable - example below

Your Turn ...

Your Turn ...

Video: Value and reference