JavaScript - Intro

Question 1

Explain Java vs. JavaScript

Answer 1

• Both use dot syntax to drill down into nested objects.
• Syntax is very similar.
• Java is an object oriented programming language developed by Sun Microsystems that is capable of running on multiple operating systems with the use of an interpreter.
• JavaScript, on the other hand, was created by Netscape as a scripting language. It cannot create stand alone applications, but instead resides within the browser.

Question 2

Even though JavaScript is described as an ______- oriented language, there are no _______. It supports object-oriented programming by using object ________. (While ES6 has a class keyword, it is syntactic sugar over a prototype based structure)

Answer 2

Even though JavaScript is described as an object-oriented language, there are no classes. It supports object-oriented programming by using object prototypes. (While ES6 has a class keyword, it is syntactic sugar over a prototype based structure)

Question 3

Everything inside of JavaScript is an ______. There are no clear distinctions between _____ and _______.

Answer 3

Everything inside of JavaScript is an object. There are no clear distinctions between types and objects.

Question 4

Java is _____-based. Objects are divided into _____ and _______ with all inheritance through the class hierarchy.

Answer 4

Java is class-based. Objects are divided into classes and instances with all inheritance through the class hierarchy.

Question 5

In JavaScript, _____ and ________ can be added to any object dynamically.

Answer 5

In JavaScript, properties and methods can be added to any object dynamically.

Question 6

n Java, ______ and ______ cannot have properties or methods added dynamically.

Answer 6

In Java, classes and instances cannot have properties or methods added dynamically.

Question 7

JavaScript is ______ typed. I can assign a String to a variable that was previously a number.

Answer 7

JavaScript is loosely typed. I can assign a String to a variable that was previously a number.

Question 8

JavaScript objects are _______ arrays. Properties can be accessed via:

Answer 8

JavaScript objects are associative arrays.

Properties can be accessed via: obj.prop or obj[‘prop’].

Question 9

JavaScript functions are _____ class members. They can be treated like ______ (can be assigned to ______ and passed around like ________)

Answer 9

JavaScript functions are first class members. They can be treated like objects (can be assigned to variables and passed around like variables)

Question 10

JavaScript does not have to be _______.

Answer 10

JavaScript does not have to be compiled.

Question 11

JavaScript’s access (through the browser) to the _____ system, _______, ________ on the machine etc is limited.

Answer 11

JavaScript’s access (through the browser) to the file system, databases, hardware on the machine etc is limited.

Question 12

To add Javascript to your page:

Answer 12

Use script tags in the or . e.g. alert(“Hello World!”);

Separate file.using script tags. e.g. The type attribute is not absolutely required on the html5 spec.

Question 13

Many developers put their script files at the _____ of the page, just before the closing body tag.

Answer 13

Many developers put their script files at the bottom of the page, just before the closing body tag.

It may improve performance and allows your page to load before it tries to access elements of your page.

Question 14

If you need your JavaScript to run before the page loads, put your script files at the ______. If you need it to run before (or after) loading an element in your page, put it where you need it.

Answer 14

However, if you need your JavaScript to run before the page loads, put it at the top. If you need it to run before (or after) loading an element in your page, put it where you need it.

Question 15

Ways to debug in Javascript:

Answer 15

• alert() is convenient but obtrusive
• Use console.log(); and the console in Chrome developer tools
• Chrome developer tools can be used to view and manipulate elements and css, execute code, debug code, view resources, network timeline, request/response details, performance and profiling.

Question 16

Variables hold ____ or different _____. Here is an example of defining a variable using the var keyword:

Answer 16

Variables hold values or different types.

Example:
//An example of variable definition using var
var x = 7; //integer (number)
x = 3.14 //float (number)
x = "Hello!"; //String
x = false; //Boolean
x = ["I", "am", "an", "array"]; //array
x = {name:"IMM", courses:10, awesome:true} //object

Question 17

List of types of values:

Answer 17

Number
String
Boolean
Array
Object
Function
Date
RegExp (used for pattern matching)
null (intentional absence of a value)
undefined (absence of a value;)

Question 18

There are three keywords we need to be aware of: ____, _____ and ____.

Answer 18

var x = "IMM"; 
let x = "IMM"; 
const x= "IMM";

Question 19

let has ____-level scope.
Var has _____-level scope.
const has _____-level scope and cannot be re-assigned a different value.

Answer 19

let has block-level scope.
Var has function-level scope.
const has block-level scope and cannot be re-assigned a different value.

Question 20

Always use the ______ keyword to define variable. Omitting that keyword will make your variable ______ and that may have unintended consequences.

Answer 20

Always use the var keyword to define variable. Omitting that keyword will make your variable global and that may have unintended consequences.

Question 21

5+5 == ?
5+”5” == ?
5*“x” == ?

Answer 21

5+5 == 10
5+”5” == “55”
5*“x” == NaN (Not a Number)

Question 22

if statement (SYNTAX)

Answer 22

if(condition){

}else{

}

Question 23

Operators:

equal to 
less than or equal to 
more than or equal to 
less than 
more than 
identical to 
not identical to 
equal to 
not equal to

Answer 23

equal to ==
less than or equal to <=
more than or equal to >=
less than <
more than >
identical to ===
not identical to !==
equal to ==
not equal to !=

Question 24

The difference between _____ and ______ rests in automatic type conversion. e.g. true == 1 and “2” == 2 but they are not identical.

Answer 24

The difference between equality and identity rests in automatic type conversion. e.g. true == 1 and “2” == 2 but they are not identical.

Question 25

String literals may be _____ to value of their _____ object counterparts but they are not _______ since they are a different type.

Answer 25

String literals may be equal to value of their String object counterparts but they are not identical since they are a different type.

Question 26

Boolean values evaluate to ____ for the following values: false, 0, empty strings (“”), NaN, null, and undefined.

All other values evaluate to _____.

Answer 26

Boolean values evaluate to false for the following values: false, 0, empty strings (“”), NaN, null, and undefined.

All other values evaluate to true.

Question 27

and: ?
or: ?
() Parentheses are used to group _____ _______.

Answer 27

and &&
or ||
() Parentheses are used to group complex comparisons

Question 28

All loops need to have an _____ that must be initialized, an ______ and a _______.

Answer 28

All loops need to have an index that must be initialized, an increment and a condition.

Question 29

while loop:

Answer 29

while(condition){
	//do this
}

Question 30

do, while loop:

Answer 30

do{
	//do this       
} while(condition)

statements within this loop gets executed at least once

Question 31

for loop:

Answer 31

for(var i=0; i<10; i++){
	//do something      
}

Question 32

for… of loop:

Answer 32

for (const currentValue of a) {
  // Do something with currentValue
}

Question 33

The keyword “_____” jumps out fo the loop entirely. The keyword continue will skip the rest of the iteration for that iteration of the loop.

Answer 33

The keyword “break” jumps out fo the loop entirely. The keyword continue will skip the rest of the iteration for that iteration of the loop.

Question 34

Create an array:

Answer 34

var arr = new Array();
var arr = []; //preferred literal syntax

Question 35

You can initialize an array with an ______ length although that length can be changed anytime.

Answer 35

You can initialize an array with an initial length although that length can be changed anytime.

var arr = new Array(5);

You can assign values using literal syntax.

var students = [“wasim”, “joe”, “Sam”];

Question 36

Another way of writing an array:

Answer 36

var students = [];   
 students[0] = "wasim"; 
 students[1] = "joe";
 students[2] = "Sam";

Question 37

Arrays may contain different types.

Answer 37

var studentInfo = [“George”, 181, true];

Question 38

Add values to the end of an array:

Answer 38

Add values to the end of an array: arrayObject.push();

Question 39

Return and remove last value in an array:

Answer 39

Return and remove last value in an array: arrayObject.pop();

Question 40

Extract values from an array: __________; begins extraction at index and ends at index 3

Answer 40

Extract values from an array: arraObject.slice(1,3); begins extraction at index and ends at index 3

Question 41

Find values in an array: ___________

Answer 41

Find values in an array: arrayObject.indexOf(“searchItem”);

Question 42

Math Object:

Answer 42

var flooredNumber = Math.floor(number); //returns the integer value of the number
var randomNumber = Math.random(); //returns a random number between 0 and 1

Question 43

Date Object:

Answer 43

var today = new Date(); //returns new date object based on today's date 
var notToday = new Date(2012,11,09); retuens a new date based on 9th Nov 2012.
dateObject.getMonth(); //returns the month
dateObject.getDay(); //returns the day
dateObject.setFullYear(2020,10,3); //sets the year, month and day of the current date object.
dateObject.getTime(); //returns the time,in milliseconds since Jan 01, 1970

Question 44

Common escape sequences:

Answer 44

\n new line
\t tab
\ backslash