topics: javascript|web workers, level: 100

What best describes a Web Worker?

Please select exactly one correct alternative.

A Web Worker is a JavaScript that runs when a callback function has been set by using setInterval. A Web Worker is a Java app that runs in the background, independently of other apps, without affecting the performance of the page. A Web Worker is a JavaScript that runs in the background, independently of other scripts, without affecting the performance of the page. None of the above.

Answer

A Web Worker is a JavaScript that runs in the background, independently of other scripts, without affecting the performance of the page. You can continue to do whatever you want: clicking, selecting things, etc., while the web worker runs in the background.

Reading

HTML5 Web Workers

topics: javascript, level: 100

What does

"use strict";

in your JavaScript code mean?

Please select exactly one correct alternative.

This defines that your browser should use only load sites using https "strictly". This defines that JavaScript code should be executed in "strict mode". It doesn't mean anything; it should be

use strict;

. None of the above.

Answer

"use strict" defines that JavaScript code should be executed in "strict mode". With strict mode, you can not, for example, use undeclared variables.

Reading

JavaScript Use Strict
Strict mode

topics: javascript|scope, level: 100

Which statements below are correct on scopes and variables?

Please select exactly one or more correct alternatives.

Global variables are not deleted when you close the page. You can still access them in pages that are hyperlinked to the page in which the variable has been declared. With JavaScript, the global scope is the complete JavaScript environment. In HTML, the global scope is the window object: All global variables belong to the window object. Your global variables (or functions) can overwrite window variables (or functions). Any function, including the window object, can overwrite your global variables and functions.

Answer

Please see the correct answer above.

Reading

JavaScript Scope

topics: javascript, level: 100

What is the difference between

split()

and

splice()

?

Please select exactly one correct alternative.

split()

operates on strings and

splice()

operates on arrays.

split()

operates on arrays and

splice()

operates on strings.

splice()

and

split()

perform exactly the same operation. None of the above.

Answer

split()

operates on strings and

splice()

operates on arrays.

Reading

Array.prototype.splice()
String.prototype.split()

topics: javascript|external scripts, level: 100

How does your browser handle this?

How does your browser handle an external JavaScript when neither defer nor asyn is present in

<script src="myscript.js"></script>

?

Please select exactly one correct alternative.

The script is fetched and executed after the browser has finished parsing the page. The script is fetched and executed immediately, before the browser continues parsing the page. The script is fetched but not executed, immediately, before the browser starts parsing the page. None of the above.

Answer

If neither async or defer is present: The script is fetched and executed immediately, before the browser continues parsing the page.

Reading

HTML <script> async Attribute
HTML <script> defer Attribute

topics: javascript, level: 100

What is

async

used for?

What is

async

in

<script src="myscript.js" async></script>

used for?

Please select exactly one correct alternative.

The script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing). The script is executed synchronously with the rest of the page (the script will be executed after the page finished parsing). The script is executed synchronously with the rest of the page (the script will be executed before the page finished parsing). None of the above.

Answer

async

Indicated that the script is executed asynchronously with the rest of the page (the script will be executed while the page continues the parsing).

Reading

HTML <script> async Attribute

topics: javascript, level: 100

What will this code do?

Consider the following code:

<script>

 myFunction();
 
    function myFunction() {
        alert(vMyVar);
    }
 
    var vMyVar = "Hello HansR!";

</script>

What will this result into?

Please select exactly one correct alternative.

It gives an alert "Hello HansR!" It gives an alert "undefined" It throws an error: "ReferenceError: vMyVar is not defined" None of the above.

Answer

The variable has not been given a value before you used it, so the value is undefined.

Reading

JavaScript Scope

topics: javascript, level: 100

What will this code do?

Consider the following code:

<script>

    vMyVar = "Hello HansR!";
 
 myFunction();
 
    function myFunction() {
        alert(vMyVar);
    }

</script>

What will this result into?

Please select exactly one correct alternative.

It gives an alert "Hello HansR!" It gives an alert "undefined" It throws an error: "ReferenceError: vMyVar is not defined" None of the above.

Answer

You correctly declared the variable and have given it a value. So it will display this value.

Reading

JavaScript Scope

topics: javascript, level: 100

Which code fragment presents a correct way to walk through an array?

Please select exactly one correct alternative.

for (vIndex = 1; vIndex <= vArray.length; ++vIndex) {}

for (vIndex = 0; vIndex < vArray.length; ++vIndex) {}

for (vIndex = 0; vIndex <= vArray.length; ++vIndex) {}

for (vIndex = 1; vIndex < vArray.length; ++vIndex) {}

None of the above.

Answer

Array indices go from 0 to length - 1 in JavaScript.

Reading

JavaScript Arrays

topics: javascript, level: 100

What is

defer

used for?

What is

defer

in

<script src="myscript.js" defer></script>

used for?

Please select exactly one correct alternative.

It indicates that the script will run only after you use a function that has been defined in it. It indicates that the script will run before the page loads. It indicates that the script will not run until after the page has been loaded. None of the above.

Answer

defer

Indicates that the script will not run until after the page has been loaded.

Reading

HTML <script> defer Attribute

topics: javascript, level: 100

How can you test whether a variable is undefined?

Please select exactly one correct alternative.

if (vMyVar == undefined) { vMessage = "vMyVar undefined"; } else { vMessage = "vMyVar defined"; }

if (vMyVar == "undefined") { vMessage = "vMyVar undefined"; } else { vMessage = "vMyVar defined"; }

if (vMyVar === undefined) { vMessage = "vMyVar undefined"; } else { vMessage = "vMyVar defined"; }

None of the above.

Answer

if (vMyVar === undefined) { vMessage = "vMyVar undefined"; } else { vMessage = "vMyVar defined"; }

method. The

unshift()

method. The

shift()

method. None of the above.

Answer

The push() method adds new items to the end of an array.

Reading

JavaScript Array push() Method

topics: javascript|variables, level: 100

What does the

unshift()

method do?

Please select exactly one correct alternative.

Adds new items to the beginning of an array. Adds new items to the end of an array. Removes items from the beginning of an array. Removes items from the end of an array.

Answer

The unshift() method adds new items to the beginning of an array.

Reading

JavaScript Array unshift() Method

topics: javascript|expressions, level: 100

What value is valid considering the pattern

"/\d{3,4}/g"

?

Please select exactly one correct alternative.

1 10 100 None of the above.

Answer

The expression checks for number strings of 3 to 4 digits.

Reading

JavaScript Regular Expressions

topics: javascript, level: 100

What will this code do?

Consider the following code:

<script>

    function myFunction() {
        vMyVar = "Hello HansR!";
    }
    
    alert(vMyVar);

</script>

What will this result into?

Please select exactly one correct alternative.

It gives an alert "Hello HansR!" It gives an alert "undefined" It throws an error: "ReferenceError: vMyVar is not defined" None of the above.

Answer

You have not defined the variable, so your browser will throw an error on it.

Reading

JavaScript Scope

topics: javascript|syntax, level: 100

What are advantages of putting your JavaScript code into an external .js file?

Please select exactly one or more correct alternatives.

Cached JavaScript files can speed up page loads. It separates HTML and code. It makes HTML and JavaScript easier to read and maintain. JavaScript will be processed much faster.

Answer

Placing JavaScripts in external files has some advantages:

It separates HTML and code.
It makes HTML and JavaScript easier to read and maintain.
Cached JavaScript files can speed up page loads.

Reading

JavaScript Where To

topics: javascript,javascript|promise, level: 100

What is a JavaScript promise?

Please select exactly one correct alternative.

The internal name of the Microsoft http service version in JavaScript. A pattern for handling asynchronous operations. A pattern for handling ftp calls. None of the above.

Answer

An AngularJS promise (or just a JavaScript promise) is a way for handling asynchronous operations.

Reading

Promise

topics: javascript|array, level: 100

Which method should you use when you want to delete an entry in a JavaScript array?

Please select exactly one correct alternative.

Answer

Please see the correct answer above.

Reading

No resources given.

topics: javascript, level: 100

How can you minimize the global namespace pollution in JavaScript?

Please select exactly one correct alternative.

By using the "namespace" keyword and define your variables within that namespace. By using a prefix followed by an underscore in-front of your variable names. By creating an Singleton Object and define your variables as member of that object. By using uppercase for all your variable names.

Answer

Please see the correct answer above.

Reading

No resources given.

topics: javascript|output, level: 100

Which of the following statements are correct on JavaScript output functions?

Please select exactly one or more correct alternatives.

The

window.alert

function writes text to a popup window. The

document.write

function writes text to the HTML output. The

console.log

function writes text to the browser console. The

console.log

function writes text to the browser console, except in IE, which gives an error message.

Answer

Please see the correct answer above.
When using the

console.log

function in IE, please make sure that the console has been opened first. If not, IS will give an error message.

Reading

JavaScript Output

topics: javascript, level: 100

Which of the below are correct statements on JavaScript?

Please select exactly one or more correct alternatives.

JavaScript is a dynamic computer programming language. JavaScript is a language for client-side scripts to interact with the user, control the browser, communicate asynchronously, and alter the document content that is displayed. JavaScript is a variant of the Java programming language. JavaScript needs to be compiled before usage in web pages.

Answer

You can use the sites below to learn about this topic.

Reading

JavaScript

topics: javascript|libraries, level: 100

What is Modernizr and what is it's purpose?

Please select exactly one correct alternative.

Modernizr is a JavaScript library that automatically optimizes your JavaScript code. Modernizr is a JavaScript library that detects mobile features in the user's browser. Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user's browser. None of the above.

Answer

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user's browser.
Taking advantage of cool new web technologies is great fun, until you have to support browsers that lag behind. Modernizr makes it easy for you to write conditional JavaScript and CSS to handle each situation, whether a browser supports a feature or not.

Reading

http://modernizr.com

topics: javascript, level: 100

What is the

splice()

function used for?

Please select exactly one correct alternative.

The splice() method changes the content of a string by removing existing elements and/or adding new elements. The splice() method changes the content of an array by removing existing elements and/or adding new elements. The splice() method splits a string into an array of elements using divider characters, like ',', in the source string. None of the above.

Answer

The splice() method changes the content of an array by removing existing elements and/or adding new elements, as in the example below.

var vMyArray = ["First", "Second", "Third"];
vMyArray.splice(2, 0, "New third", "New fourth");

The result of vMyArray will be:

First,Second,New third,New fourth,Third

Reading

JavaScript Array splice() Method

topics: javascript|timing, level: 100

What is the difference between

setTimeout

and

setInterval

?

Please select exactly one correct alternative.

setTimeout Execute a given function once and setInterval schedules a repeating execution of that function. setInterval Execute a given function once and setTimeout schedules a repeating execution of that function. Both setInterval and setTimeout do exactly the same: schedule a repeating execution of a given function. None of the above.

Answer

Both functions execute a given function in a given time. But setTimeout only executes this function once, while setInterval schedules a repeating execution.

Reading

Understanding timers: setTimeout and setInterval

topics: javascript|functions, level: 100

What is a self invoked function?

Please select exactly one correct alternative.

A function that is stored within a JavaScript variable. A function that is automatically called when loaded. A self invoked function does not exist in the JavaScript context. None of the above.

Answer

A self invoked function is a function that is stored within a JavaScript variable.

Reading

JavaScript Function Definitions

topics: javascript|syntax, level: 100

Which are correct examples for comments in JavaScript?

Please select exactly one or more correct alternatives.

// This is a comment.

<!--> This is a comment. <-->

<!-- This is a comment. -->

<% This is a comment. %>

/* This is a comment. */

Answer

Comments can be placed in between  or after // in JavaScript.

Reading

JavaScript Comments

topics: javascript|syntax, level: 100

Where can you place your JavaScript in your web page?

Please select exactly one correct alternative.

Scripts can be placed in the

<body>

, or in the

<head>

section of an HTML page. Scripts can be placed in the

<body>

, or in the

<head>

section of an HTML page, or in both. Scripts can be placed in the

<body>

, in the

<head>

section of an HTML page, or just before the

<html>

tag, or in all three locations. None of the above.

Answer

Scripts can be placed in the <body>, or in the <head> section of an HTML page, or in both.

Reading

JavaScript Where To

topics: javascript, level: 100

Which of the below are correct statements on JavaScript?

Please select exactly one or more correct alternatives.

JavaScript is a dynamic computer programming language. JavaScript is a language for client-side scripts to interact with the user, control the browser, communicate asynchronously, and alter the document content that is displayed. JavaScript is a variant of the Java programming language. JavaScript needs to be compiled before usage in web pages.

Answer

Please see the resources below.

Reading

JavaScript

topics: javascript|operators, level: 100

What is the difference between

==

and

===

in JavaScript expressions?

Please select exactly one correct alternative.

Both operators have exactly the same meaning.

===

Means: equal value and equal type

==

Means: equal value and equal type None of the above.

Answer

=== Means: equal value and equal type, == only means equal.

Reading

JavaScript Comparison and Logical Operators

topics: javascript, level: 100

Which code fragment presents a correct way to walk through an array?

Please select exactly one correct alternative.

(vIndex = 0; vIndex < vArray.length; ++vIndex)

for (vIndex = 1; vIndex <= vArray.length; ++vIndex)

for (vIndex = 0; vIndex <= vArray.length; ++vIndex)

for (vIndex = 1; vIndex < vArray.length; ++vIndex)

Answer

An index for a JavaScript array runs from 0 to length - 1. Hence, the correct way to walk through an array is:

(vIndex = 0; vIndex < vArray.length; ++vIndex)

.

Reading

No resources given.

topics: javascript|expressions, level: 100

What value is valid considering the pattern

"/\d{3,4}/g"

?

Please select exactly one correct alternative.

1 10 100 None of the above.

Answer

The expression checks for number strings of 3 to 4 digits.

Reading

JavaScript Regular Expressions

topics: javascript, level: 100

Which statements are correct on

null

,

empty

and

undefined

in JavaScript?

Please select exactly one or more correct alternatives.

undefined

means a variable has been declared but has not yet been assigned a value.

null

is an assignment value. It can be assigned to a variable as a representation of no value.

undefined

and

null

are two distinct types.

null

is an object

null

is the same as 0.

empty

is the same as undefined.

empty

is not defined in JavaScript.

Answer

Please see the correct answer above.

Reading

No resources given.

topics: javascript|timing, level: 100

Why is it not recommended to have many setInterval / setTimeout at the same time?

Please select exactly one correct alternative.

They cost a lot of CPU time. This could make your browser slow. They cost a lot of memory. This could make your machine slow. They cost a lot of diskspace. This could make your machine crash. None of the above.

Answer

They cost a lot of CPU time. This could make your browser slow. Ofcourse, this depends on the processing power of your machine. In general, mobile devices are slower than e.g. desktop devices. It is preferred that a single setInterval / setTimeout call manages multiple animations.

Reading

Understanding timers: setTimeout and setInterval

That's all folks!

Congratulations, you've made it to the end! I'll try to add more questions and topics on a regular basis.

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