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Examination Questions

Note: The competency table is written in such a way as to make it easy to construct additional examination questions.

JavaScript History and ECMAScript characteristics

  • Explain how the terms ECMAScript, JavaScript, ActionsScript and JScript relate to each other.
  • What languages have influenced JavaScript? How?
  • What is the Document Object Model (DOM)?
  • Explain the terms DHTML, DOM scripting and Ajax.
  • List three implementations of ECMAScript outside of web browsers.
  • What is the difference between an interpreted and a compiled programming language?

DOM Scripting best practices (overview)

  • Summarize the concepts of “graceful degradation”, “progressive enhancement” and “unobtrusive scripting”.
  • What characterizes well written JavaScript?

ECMAScript lexical structure

  • In programming, what is a statement?
  • What terminates a statement in JavaScript?
  • To what family of programming languages does JavaScript belong, looking at how to construct compound statements?
  • Write out an XHTML comment? A JavaScript comment in two ways?
  • Give an example of o common error caused by JavaScript being case-sensitive.

ECMAScript data types and variables

  • List and define the data types available in JavaScript?
  • Define the term “variable” as it relates to JavaScript.
  • Explain the rules of identifiers in JavaScript.
  • What is weak typing?
  • How does JavaScript do boolean conversions?
  • Explain why "1" + 1 == 11
  • Why is 1 == "1" but not 2 === "2"?
  • What variable scopes are available in JavaScript?
  • Which versions of JavaScript have got block scope? What is it and how do you use it?
  • Summarize the concept of garbage collection

Expressions and Operators

  • What are JavaScript operators and how are they used?
  • Explain arity.
  • Explain how operator associativity and priority work in ECMAScript.
  • Write an if-else statement and make a ternary operator expression with identical functionality.
  • What is the difference between assignment by value and assignment by reference? When does the latter occur in JavaScript?
  • What does the operators typeof and instanceof do?
  • Why is it troublesome to typecheck an array with typeof?
  • Construct an expression using post- and pre- incrementation.

Control Structures

  • Define the purpose of the var keyword.
  • Define the purpose of a conditional statement.
  • Define the purpose of a repeat loop.
  • What are exceptions? How do one throw and catch exceptions?

Strings and String Functions

  • How does javaScript internally represent strings?
  • What is concatenation?

Objects and Arrays

  • In JavaScript, what is an object? An array?
  • What are Array and Object literals?
  • Explain the difference between dot notation and bracket notation.
  • Being classless, how does JavaScript support inheritence?
  • What array-like (i.e. similar to but not being true arrays) objects does ECMAScript and the DOM have?


  • What is a function?
  • What does the return statement do?
  • What is lambda?
  • In JavaScript functions are first class objects; explain.
  • What is a parameter or “argument” and how is it related to a function?
  • What is the arguments property of a function? How can it be used?
  • What is a closure?

Regular expressions

  • Explain regular expressions.

The Date Object

  • Briefly explain the usage of the Date object

Numbers and the Math object

  • What is a Number in JavaScript?
  • Does javaScript differentiate between integer and decimal data types?
  • How can a value be converted to a number?
  • How can a value be checked to see if it is a number?
  • How can a number be rounded to a given precision?
  • What is the purpose of the Math object?

Programming concepts

  • What programming paradigms can be supported by JavaScript?
  • Explain iteration, enumeration and recursion.
  • JavaScript usually does not have standard streams, but a global object; explain.
  • What are the naming conventions regarding constructor objects in JavaScript?
  • What is a Run Time Environment?
  • Explain the concept of namespaces and demonstrate some ways of working around the lack of namespaces in ECMAScript 3 and 5th edition

Client side DOM Scripting/Properties and methods of the window Object

  • How can one add scripts to an (X)HTML page? Give several examples and discuss their benefits and what ways should be avoided?
  • What is the window object.
  • List at least 5 commonly used properties or methods of the window object.
  • Write a few lines of realistic client side JavaScript and explain what parts are ECMAScript and what parts are the DOM.
  • List all major standards that apply to the DOM and the BOM and briefly state what is covered by each standard.

The Document Object Model

  • Construct a simple (X)HTML document and graph out the equivalent DOM structure.
  • What is a node? What types of nodes are there?
  • Define childNodes, firstChild, and lastChild properties.
  • What is PCDATA and CDATA?
  • What is the Document Element?

DOM Support

  • What is capability testing? Why is it important? How is it superior to browser sniffing?
  • Write a line of DOM Script that demonstrates how to capability test.

Accessing DOM Elements

  • Show how to access elements in the DOM in at least five different ways.
  • Compare setting and getting attributes, using DOM Core methods as well as DOM HTML methods.
  • What are “collections” in the DOM?

DOM and Class and Style Manipulation

  • Why should the document.write() method be avoided?
  • When using innerHTML in a pure XHTML page, what limitations apply?
  • How can one access the text content of an element?

Manipulating the DOM

  • How are elements constructed an added to the DOM using DOM Core methods?
  • List and briefly explain at least three good practices to get fast script execution when manipulating the DOM or changing styles dynamically.
  • HTML 5 adds a new special attribute intended for storing arbitrary data; what are those attributes and how can they be accessed?


  • What are the leading DOM Scripting libraries? In a sentence or two descibe their design principles.


  • What are DOM 0 event handlers?
  • What are DOM 2 event listeners? What benefits do they have compared to event handlers?
  • Internet Explorer up to and (at least) including 8.0 does not support W3C events; what does it have instead?
  • Explain event capturing/bubbling.
  • Some events are troublesome due to cross browser inconsistencies and bugs. Give an example and explain ways of working around it.
  • Explain at least three ways of making sure the DOM is loaded before code is executed.

Timed events

  • The window object has four methods that apply to timed events, what are they and how do you use them?

Form handling

  • List the most commonly used form events (at least 3).
  • Explain how to access the value of a radio button based field in a form.


  • What is Ajax?
  • List some common usability problems caused by badly written Ajax scripts (at least 3).


  • What kind of disabilities or technological limitations must a developer of a web site take into consideration?
  • What is ARIA? How can ARIA be used to facilitate accessibility on scripted pages?

Common DHTML mistakes and security

  • DHTML of the 90's gave JavaScript a bad reputation. List some common mistakes that contributed to this fact.
  • What is Cross Site Scripting?
  • JavaScript guru Douglas Crockford warns against “hidden uses of eval”; explain.