• Unit 5: The Basics of Functions

    This unit introduces basic function declarations or function statements. We'll cover more advanced topics in the subsequent courses. Functions perform a specific task and make your program modular, not one large chunk of code. The JavaScript language has many "built-in functions" that perform math, string, or date operations. JavaScript also allows you to develop your functions.

    Completing this unit should take you approximately 2 hours.

    • Upon successful completion of this unit, you will be able to:

      • identify types of functions;
      • use function with arguments;
      • compare types of function declarations; and
      • write code that calls functions.

    • 5.1: Functions to Perform a Task in Action

      • Introduction to Functions Page

        This video provides an introduction to functions. Functions eliminate the need to write the same code repeatedly, which saves time. Functions also make your code much more manageable by segmenting a huge program into a number of functions, which makes modification efficient.

      • JavaScript Functions Book

        Functions are objects in JavaScript and can be used as variables in expressions, passed to other functions, or treated like numbers or strings.

        The traditional function declaration has several parts:

        • function keyword;
        • name of the function;
        • function body, which contains JavaScript statements; and
        • return statement

        Functions may have "parameters", values passed to the function from a calling program, but they are not required. To execute a function, it must be "called". This will run the statements in the body of the function. Read this article about how functions are defined and used. After reading this article, consider these questions: 

        • What is the difference between local, global, and lexical scoping?
        • Can functions be called with different numbers of parameters?
        • What is returned if a function does not have a "return" statement?

    • 5.2: Declaring Functions

      • Function Declaration Notation Page

        There are several ways to define a function in JavaScript. We'll start by looking at the syntax (rules) for the traditional function declaration or function statement. It uses function name, parameters, and statement(s). Notice that function declarations can be hoisted, which means they can be called before they are declared.

    • 5.3: Additional Function Declarations

      • Function Expression Notation Page

        JavaScript supports additional ways to define a function. This article describes the syntax for a "function expression". A function expression declares a variable and then assigns it to the function. That is, it is defined within the statement and does not need to be "called". Function expressions do not support hoisting.

      • The Arrow Function Page

        Another way to define a function is by using the fat arrow (=>). This article describes the syntax for the "arrow function" and compares it to the traditional or named function. The fat arrow is an ES6 (ECMAScript) notation, and support may not be in some browsers. ECMAScript is a specification for scripting languages, and JavaScript conforms to this specification. In addition, ES6 introduced features found in other languages, such as classes, the const keyword, and Unicode. You can learn more about the ES6/2015 specification at this link.

      • Example in Action: JavaScript Functions Expression and Arguments Page

        Watch this video that uses the function by expression notation to output a person's name. Try this example using an online editor or an editor of your choice. Remember to use one of the Linter programs if you have syntax errors in the program.

      • Practice Review: Using Functions with Conditionals Page

        Try this exercise to see how well you understood working with functions and conditionals. Copy the code into your favorite editor and display an "interactive" web page that uses a function and a "while" statement to compute the current speed. This exercise does not count towards your grade. It is just for practice!

    • Study Session Review Video

    • Unit 5 Assessment

      • Unit 5 Assessment Quiz
        Receive a grade

        Take this assessment to see how well you understood this unit.

        • This assessment does not count towards your grade. It is just for practice!
        • You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
        • You can take this assessment as many times as you want, whenever you want.