A
Your application prompts the user to enter his or her age, which is placed in an age
variable. A user ran the application and entered I Don’t Know for the age. The application
then multiplies age by two. What is the result?
A. undefined
B. null
C. NaN
D. infinity
Correct answer: C
A. Incorrect: The undefined value means that the variable has never been initialized.
B. Incorrect: The null value means that the variable was explicitly set to have no
value.
C. Correct: When performing a mathematical operation on a nonnumeric value, NaN
(not a number) will result.
D. Incorrect: The Infinity value will result when your value exceeds
1.7976931348623157E + 10308.
Where should your JavaScript code be placed?
A. In the <head> element of your HTML document.
B. Just before the </body> tag.
C. You should always place your JavaScript code in separate files, external to your
HTML document.
D. Inside the <body> element, at the top.
Correct answer: C
A. Incorrect: Placing your JavaScript code in the <head> element does not promote
reuse, and inline code might reference elements that are not yet loaded.
B. Incorrect: Placing your JavaScript code in the </body> tag does not promote
reuse.
C. Correct: Placing your JavaScript code in separate files, external to your HTML
document, promotes reuse.
D. Incorrect: Placing your JavaScript code in the <body> element does not promote
reuse, and inline code might reference elements that are not yet loaded.
How is inheritance supported in JavaScript?
A. You replace the prototype of the child object with a new instance of the parent
object and then replace the prototype constructor with the child constructor.
B. You call the createChild method on the parent object.
C. You call the setParent method on the child object.
D. JavaScript does not support inheritance.
Correct answer: A
A. Correct: You replace the prototype of the child object with a new instance of
the parent object and then replace the prototype constructor with the child
constructor.
B. Incorrect: The createChild method is not a valid method.
C. Incorrect: The setParent method is not a valid method.
D. Incorrect: JavaScript does support inheritance by replacing the prototype of the
child object with a new instance of the parent object and then replacing the prototype constructor with the child constructor.
Which method creates a resolved promise object?
A. resolve()
B. done()
C. $.when()
D. $.Deferred().
Correct answer: C
A. Incorrect: The resolve method resolves an existing promise object, but it doesn’t
create a new resolved promise object.
B. Incorrect: The done method executes code upon success of a promise object, but
it does not create a resolved promise object.
C. Correct: The $.when() method creates a resolved promise object.
D. Incorrect: The $.Deferred() method creates an unresolved promise object.
Which of the following represent valid variable declarations? (Choose all that apply.)
A. var switch;
B. var myChar;
C. var $cost;
D. var _total;
E. var 1to1;
F. var tooGood4u;
Correct answers: B, C, D, and F
A. Incorrect: You cannot use a JavaScript keyword for a variable name, and switch is a
JavaScript keyword.
B. Correct: The myChar variable name is valid.
C. Correct: JavaScript allows a variable name to contain the dollar sign, so the $cost
variable name is valid.
D. Correct: JavaScript allows a variable name to contain the underscore, so the _total
variable name is valid.
E. Incorrect: Variable names cannot begin with a number.
F. Correct: Variable names can contain numbers but cannot begin with a number.
You have two arrays of strings, customers and employees, and you want to combine
them to create a contacts array. Which method would be most suitable for this task?
A. concat
B. join
C. push
D. splice
Correct answer: A
A. Correct: Concat concatenates multiple arrays and produces a resultant array.
B. Incorrect: Join creates a string from the items in the array.
C. Incorrect: Push adds a single item to the end of the array.
D. Incorrect: Splice adds and removes items from an array and produces a resultant
array, but you must add the items one by one, not as an array.
You want to locate all the elements on your webpage that are assigned the CSS class
name Hidden. Which jQuery statement can you use?
A. var hidden = $ (‘#Hidden’);
B. var hidden = $ (‘.Hidden’);
C. var hidden = $ (‘Hidden’);
D. var hidden = $(‘class=Hidden’);
Correct answer: B
A. Incorrect: The use of the hash (#) symbol in the CSS selector indicates that you
want to locate an element based on its id.
B. Correct: The use of the period (.) in the CSS selector indicates that you want to
locate the elements that match the CSS class name.
C. Incorrect: Supplying a name for a CSS selector indicates that you want to locate
the elements that have that tag name.
D. Incorrect: The var hidden = $(‘class=Hidden’); syntax is invalid.
Which method do you call to subscribe to the successful completion of an asynchronous
operation?
A. done
B. always
C. complete
D. success
Correct answer: A
A. Correct: The done method executes code upon successful completion.
B. Incorrect: The alway method executes code regardless of success or failure.
C. Incorrect: The complete method does not exist.
D. Incorrect: The success method does not exist.
In your application, you want to display a personalized message to the user, if the
user’s name is populated, in the userName variable, but if userName is empty, you
want to use Valued User instead. How can you accomplish this most efficiently?
A. var personalized = ‘Hello ‘ + (userName ?? ‘Valued User’);
B. var personalized = ‘Hello ‘ + (userName || ‘Valued User’);
C. var personalized = ‘Hello ‘ + (userName && ‘Valued User’);
D. var personalized = ‘Hello ‘ + (userName + ‘Valued User’);
Correct answer: B
A. Incorrect: The use of ?? causes a syntax error.
B. Correct: The use of || causes Valid User to be displayed if userName has no value.
C. Incorrect: The use of && displays nothing if userName has no value.
D. Incorrect: The use of + causes Valid User to be displayed if userName has no value,
but it also displays the userName and Valid User together when the userName has
a value.
You want to obtain a list of all elements whose tag name is div, and you need to
retrieve this list as quickly as possible. Which function is most appropriate for this task?
A. getElementsByName
B. querySelectorAll
C. getElementsByTagName
D. getElementsByClass
Correct answer: C
A. Incorrect: getElementsByName retrieves a live NodeList of elements based on the
element’s name attribute, not on the tag name.
B. Incorrect: querySelectorAll is capable of retrieving the elements by tag name, but
returns a static NodeList, which does not perform as well as functions that return a
live NodeList.
C. Correct: getElementsByTagName retrieves a live NodeList of elements based on
the element’s tag name.
D. Incorrect: getElementsByClass retrieves a live NodeList of elements based on the
CSS class name.
You are interested in writing event-driven JavaScript code that will work on most
browsers without writing browser-specific code. How can you accomplish this?
A. Use the jQuery library to help.
B. Use only JavaScript statements that are the same across all browsers.
C. Do not use any JavaScript.
D. It’s impossible to write event-driven JavaScript code that is not browser-specific.
Correct answer: A
A. Correct: Using jQuery will help you create event-driven, browser-independent
code.
B. Incorrect: The code for creating and subscribing to events is browser-specific.
C. Incorrect: You need to use JavaScript to write event-driven code.
D. Incorrect: Use the jQuery library to write browser-independent code.
Which method do you call on the deferred object to indicate a change in progress?
A. progress
B. notify
C. done
D. resolve
Correct answer: B
A. Incorrect: The progress method executes code when progress has changed; it does
not to indicate a change in progress.
B. Correct: The notify method indicates a change in progress.
C. Incorrect: The done method executes code when completed but does not indicate
a change in progress.
D. Incorrect: The resolve method indicates success, not a change in progress.
You are creating a new Windows 8 application, and you want to set up TDD for your
JavaScript code. Which testing framework will you use?
A. QUnit
B. QUnit-Metro
C. Microsoft Test
D. NUnit
Correct answer: B
A. Incorrect: QUnit is for testing JavaScript for the web, not Windows 8.
B. Correct: QUnit-Metro is a variation of QUint, which supports Windows 8.
C. Incorrect: Microsoft Test does not support JavaScript.
D. Incorrect: NUnit does not support JavaScript.
What is the blueprint for an object called?
A. property
B. method
C. class
D. event
Correct answer: C
A. Incorrect: A property is a variable that’s defined on an object.
B. Incorrect: A method is a function that’s defined on an object.
C. Correct: A class is a blueprint for an object.
D. Incorrect: An event takes place from external input, usually from user input.
You are interested in locating all <p> elements on your webpage, so your statement is
var paragraphs = $(‘p’). Which line of code would confirm whether at least one element
is found?
A. if( paragraphs.exists)
B. if( paragraphs==null)
C. if( paragraphs.length)
D. if( paragraphs.count > 0)
Correct answer: C
A. Incorrect: jQuery does not have an exists property.
B. Incorrect: Even if no elements are found, jQuery will return a wrapper object.
C. Correct: If no elements are found, the length property will be 0, which converts to
a Boolean false.
D. Incorrect: jQuery does not have a count property.
Explain “this” keyword in JavaScript
this” is not a variable. It is a keyword. You cannot change the value of this. It refers to the global object in all the global code.
We know, how to create the multiple objects. We can use Object Constructor function. We’ll use this keyword to create a property, which belongs to a function.
function Automobile(engine, fuel, tyres) {
this.engine = engine;
this.fuel = fuel;
this.tyres = tyres;
}
var car = new Automobile(true, true, 4);
var bike = new Automobile(true, true, 2);
This refers to the parent object in the body of the function:
var counter = {
val: 0,
increment: function() {
this.val += 1;
}
};
counter.increment();
console.log(counter.val); // 1
counter['increment']();
console.log(counter.val); // 2
What are the steps for TDD?
A. Write the passing test, write the code, run the test again to validate that it still
passes.
B. Write the failing test, write the code, run the test again to validate that it passes.
C. Write the code, write the test to validate that it passes, run the test again to validate
that it still passes.
D. Write the passing test, write the code, break the code, run the test again to validate
that it fails.
Correct answer: B
A. Incorrect: You need to write a failing test first so you can see the test pass after
you write the code.
B. Correct: You write a failing test and then write code that makes the test pass; then
run the test again to validate that it passes.
C. Incorrect: You should never write code without first writing a test that fails.
D. Incorrect: If you write a passing test first, the code cannot be tested for success.
What does JavaScript use as a starting object when constructing a new object?
A. prototype
B. property
C. class
D. event
Correct answer: A
A. Correct: The prototype is the starting object that is cloned when creating a new
object.
B. Incorrect: A property is a variable that’s defined on an object.
C. Incorrect: A class is a blueprint for an object.
D. Incorrect: An event takes place from external input, usually from user input.
Which method chains asynchronous operations?
A. pipe()
B. done()
C. resolve()
D. always()
Correct answer: A
A. Correct: Use the pipe method to chain asynchronous operations because it provides access to progress, failure, success, and complete.
B. Incorrect: The done method executes code when completed but does not provide
access to failure, progress, and complete.
C. Incorrect: The resolve method indicates success but is not used for chaining.
D. Incorrect: The always method executes on completion regardless of success or
failure. This method does not provide access to progress, success, or failure.
Explain “delete” keyword in JavaScript.
When we work on the large Applications, we work with many objects. We are familiar with the problems like memory leak, performance of an Application is not good and similar issues arise at a later stage. I always recommend, that we need to know, how much memory, are we consuming in our Application.
Ex- Chrome provides a quick way to look into the memory usage.
The main advantage is to delete an unwanted property from an object.
var automobile = {engine: true, fuel: true, tyres:2 };
var car = Object.create (automobile); //car is instanceof automobile
console.log (car.tyres); // 2 it inherits from parent class
//as we know car has own tyres then we can create own property of car object
car.tyres = 4; // will make own tyre property of car object