Javascript

Front 1

What can it do on web pages?

Back 1

Dynamically create, delete, modify the DOM structure of the HTML elements. - Change styling of the HTML elements.
- Bind event handlers on HTML elements.
- Formvalidations,handlebrowserstorage,caching

- Handleasyncrequestcallsandresponsemechanisms.
- PrettymuchanythingundertheSun(well,may noteverything)

Front 2

where to put JS in HTML?

Back 2

last elemnt of body

they actually block parallel downloads

Front 3

Where are input and output functions in JavaScript?

Back 3

none

Front 4

is JS case sensetive ?

Back 4

yes

Front 5

how to declare JS variables?

Back 5

using var

Front 6

how to find var type

Back 6

using typeof

Front 7

declare strings

Back 7

var firstName = new String('JavaScript');

OR

var firstName = 'JavaScript';

Front 8

how to get value of a var?

Back 8

valueof()

Front 9

which stands for false values?

Back 9

0, -0, null, '', undefined, NaN, false : all evaluate to false;

Front 10

boolian var decl

Back 10

var myVar = new Boolean(true);

or

var myVar = new Boolean();

Front 11

4 types of data types

Back 11

obj

numbr

string

boolean

Front 12

function of try block

Back 12

The try statement lets you test a block of code for errors

Front 13

funxn of catch block

Back 13

The catch statement lets you handle the error.

Front 14

funxn of finally block

Back 14

The finally statement lets you execute code, after try and catch, regardless of the result.

Front 15

funxn of throws keyword

Back 15

The throw statement lets you create custom errors.

Front 16

2 ways of creating an object

Back 16

var obj = new Object(); //or

var obj = {};

Front 17

show an example which illustrates that JS objects can have multiple properties and is recursive

Back 17

var obj = { name: "Carrot",

details: { color: "orange",

size: 12 }

};
console.log(obj.details.color);
console.log(obj['details']['color']);

Front 18

use of Object.keys()

Back 18

to get an array of all the keys of obj

Front 19

2 ways of declaring an array

Back 19

var arr = new Array(); //or

var arr = [];

arr[0] = 'First'; arr[1] = 'Second'; arr[2] = 50;

var arr2 = ['First', 'Second', 50]; //or
var arr2 = new Array('First', 'Second', 50);

Front 20

how can you show array.length isn't necessarily the number of items in the array?

Back 20

console.log(arr2.length); //array.length isn't necessarily the number of items in the array. var a = ["dog", "cat", "hen"];
a[100] = "fox";
console.log(a.length); //returns 101

Front 21

function of an array toString() method

Back 21

The toString() method converts an array into a String and returns the result.

Note: The returned string will separate the elements in the array with commas.

Front 22

example of an array toString() method

Back 22

Convert an array to a string:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.toString();

The result of fruits will be:

Banana,Orange,Apple,Mango

Front 23

concat(item[, itemN]) use?

Back 23

Returns a new array with the items added on to it. No change to original array.

Front 24

join() method use

Back 24

The join() method joins the elements of an array into a string, and returns the string.

The elements will be separated by a specified separator. The default separator is comma (,).

Front 25

join method example

Back 25

Example

Try using a different separator:

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var energy = fruits.join(" and ");

The result of energy will be:

Banana and Orange and Apple and Mango

Front 26

pop() method of an array

Back 26

Removes and returns the last item. Original array is modified.

Front 27

push() method of an array

Back 27

Adds one or more items to the end. Original array is modified.

Front 28

reverse() method of an array

Back 28

reverses array and modifies it

Front 29

shift()

Back 29

Removes and returns the first item. Original array is modified.

Front 30

slice(start, end)

Back 30

Returns a sub-array. No change to original array.

Front 31

sort([cmpfn])

Back 31

Sorts items and takes an optional comparison function. Original array is modified.

Front 32

splice(start, delcount[, itemN])

Back 32

Modifies an array by deleting a section and replacing it with more items. Original array is modified

Front 33

unshift([item])

Back 33

Prepends items to the start of the array. Original array is modified.

Front 34

indexOf(item [, start])

Back 34

Returns the first occurrence index of item in the array or -1 if not found.

Optional start value.

Front 35

full form of JSON

Back 35

JavaScript Object Notation

Front 36

rules for JSON

Back 36

-Keys must be strings.
- All strings must be double-quoted.
- Possible values: string, number,array,true,false,null,anotherJSONobject

Front 37

simple example for JSON

Back 37

//multiple properties and recursive

var obj = { "name": "Carrot", "details": {

"color": "orange",

"size": 12 }

};

Front 38

JSON objects must be _________________

Back 38

JSON object should be serializable i.e. convertible to a string and vice-versa.

Front 39

NativeJSONParser[IE8+]

Back 39

var str = '{"name":"JavaScript","dob":1995,"author":"Brendan Eich","company":"Netscape"}';

//String to JSON object

var obj = JSON.parse(str); console.log(obj.author); //prints Brendan Eich

//JSON object to string

var s = JSON.stringify(obj);

Front 40

how many return types do JS functions have ?

Back 40

JavaScript functions do not have return type.

· JavaScript functions can return multiple data type values.

Front 41

basic syntax of a function

Back 41

function a(){// do some work and/or return };

Front 42

example of JSON objects having funxns as properties

Back 42

Front 43

how to check if a property is a funxn

Back 43

using typeof()

Front 44

Difference between two ways of declaring functions

Back 44

Front 45

Can arguments can be accessed inside function even without specifying parameters

Back 45

Front 46

what is the scope of variables within a function?

Back 46

they (those variables that are declared inside a fnxn) can only be accessed within the funxn, not outside

Front 47

what are global variables?

Back 47

variables declard outside a fnxn

Front 48

what are global variables attached to or how can they be accessed?

Back 48

Front 49

how to access a variable that is declared inside a function?

Back 49

Front 50

who has more priority for the same name - glob vars or local vars?

Back 50

local

Front 51

what is hoisting ?

Back 51

Front 52

what can override a variable declaration when hoisted?

Back 52

Front 53

what is JS strict mode?

Back 53

Allows you to place a program, or a function, in a “strict” operating context.

· Catches some common coding bloopers, throwing exceptions.

· Throws error in unsafe actions like accessing global object without var.

· Throws error while accessing deprecated functions.

Front 54

example of strict mode

Back 54

Front 55

what are closures?

Back 55

Front 56

BOM

Back 56

browser object model

Front 57

window object

Back 57

The window object is supported by all browsers. It represent the browser's window.

All global JavaScript objects, functions, and variables automatically become members of the window object.

Global variables are properties of the window object.

Global functions are methods of the window object.

Even the document object (of the HTML DOM) is a property of the window object

Front 58

Create a

element and append it to a

element:

Back 58

http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_document_createelement4

var para = document.createElement("P"); //Create a

element
var t = document.createTextNode("This is a paragraph."); // Create a text node
para.appendChild(t); // Append the text to

document.getElementById("myDIV").appendChild(para); // Append

to

with id="myDIV"

Front 59

document.createTextNode();

Back 59

http://www.w3schools.com/jsref/met_document_createtextnode.asp

Example

Create a

element with some text:

var para = document.createElement("P"); // Create a

element
var t = document.createTextNode("This is a paragraph."); // Create a text node
para.appendChild(t); // Append the text to

Front 60

document.forms;

Back 60

The forms collection returns a collection of all

elements in the document.

Front 61

what does "document.getElementById("demo").innerHTML" do?

Back 61

http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_element_innerhtml

The innerHTML property sets or returns the HTML content (inner HTML) of an element.

Front 62

document.getElementsByName(name)

Back 62

http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_doc_getelementsbyname_loop

Front 63

what does window represent ?

Back 63

an open browser in a window

Front 64

what is an iframe?

Back 64

it is a separate window inside a window - example the output frame of plunker

Front 65

how to create new elements in JS?

Back 65

createElement()

Front 66

window.location

Back 66

location,url, hostname, etc

Front 67

window.history - all 3 of them

Back 67

window.history.go()

window.history.back()

window.history.forward()

Front 68

what are timing functions ? like for example setTimeout()

Back 68

it executes a fnxn after a certain period of time

Front 69

clearTimeout()

Back 69

The clearTimeout() method clears a timer set with the setTimeout() method.

The ID value returned by setTimeout() is used as the parameter for the clearTimeout() method.

Note: To be able to use the clearTimeout() method, you must use a global variable when creating the timeout method:

myVar = setTimeout("javascript function",milliseconds);

Then, if the function has not already been executed, you will be able to stop the execution by calling the clearTimeout() method.

http://www.w3schools.com/jsref/met_win_cleartimeout.asp

Front 70

window.open() and window.close()

Back 70

opens and closes a new window

Front 71

window.innerheight()

window.innerwidth()

Back 71

Get the window's height and width: (NOT including toolbars/scrollbars)

http://www.w3schools.com/jsref/prop_win_innerheight.asp

Front 72

full form of DOM

Back 72

document object model

Front 73

DOM nodes

Back 73

In the HTML DOM (Document Object Model), everything is a node:

* The document itself is a document node
* All HTML elements are element nodes
* All HTML attributes are attribute nodes
* Text inside HTML elements are text nodes
* Comments are comment nodes

Front 74

which html elements allow you to refresh or reload the page?

Back 74

links / anchor tags and form submission events !!!!

Front 75

local scope vs global scope

Back 75

for example we have -

var a = ......

function d (){

//something

}

this 'a' variable is declared globally and accessible everywhere throughout

however if we had --

function d {

var a = ...

// something more

}

then a - will have a local scope only restricted to that function - it might return undefined when called from outside the function

Front 76

what will be the output be? --

Back 76

Front 77

what will the output be ?

Back 77

it will be the 2nd alert message since newCustomer is false

Front 78

"Page protocol is " + window.location.protocol;

Back 78

Page protocol is http:

Front 79

Example

Display the href (URL) of the current page:

"Page location is " + window.location.href;

Back 79

Page location is http://www.w3schools.com/js/js_window_location.asp

Front 80

"Page host is " + window.location.hostname;

Back 80

Page hostname is www.w3schools.com

Front 81

what does the map funxn do ?

Back 81

the map funxn takes in another function and applies that function to member of the array, so basically u cn say it acts like an array loop

Front 82

Back 82

a doubled array

Front 83

u have the following array of names - how can you use map method to print them out as array of full names ? ---

var modifiedNames = [ "Thomas Meeks",
"Gregg Pollack",
"Christine Wong",
"Dan McGaw" ];

Back 83

var modifiedNames = passengers.map(
function (arraycell)
{
return(arraycell[0]+" "+arraycell[1]);
}
);

Front 84

make an array of functions

Back 84

var puzzlers = [
function(a) { return 3 * a - 8; },
function(a) { return (a + 2) * (a + 2) * (a + 2); },
function(a) { return a * a - 9; },
function(a) { return a % 4; }
];

Front 85

var a=[1,2,3,4]

console.log(a.shift());

what will be the output?

Back 85

1

Front 86

what will be the output when buildTicket( parkRides, fastPassQueue, wantsRide ); is called? how to change the function to an IIFE?

Back 86

To change it to an IIFE we need to put

Front 87

returning functions inside a function --

do you need () after the return statement ?

Like -

function a() {

if(...) {

return function () {........}; // Do you need a () here ?

}

}

Back 87

No

Front 88

Back 88

adventureSelector(3)();

Front 89

What happens in this code ? --

var puzzlers = [
function(a) { return 8 * a - 10; },
function(a) { return (a - 3) * (a - 3) * (a - 3); },
function(a) { return a * a + 4; },
function(a) { return a % 5; }
];
var start = 2;

var applyAndEmpty = function(input, queue) {
var length = queue.length;
for (var i = 0; i < length; i++) {
input = queue.shift()(input);
}
return input;
};

alert(applyAndEmpty(start, puzzlers));

Back 89

the queue array is emptied as it also performs operations on the numbr "start" as declared inside it ( queue is an array of functions)

Front 90

what will be the output ?

Back 90

4

Front 91

how can we access local variables, whose scope is only restricted to inside funxns?

Back 91

by using closures

Front 92

what will be the output of result ?

Back 92

40

Front 93

output of result ?

Back 93

122

Front 94

explain the concept of load order

Back 94

the first diagram looks ok - however if ( see the 2nd diagram ) the local variable is initialized or declared before sub funxn 2 and called before sub funxn 2 , the program will fail - hence the importance of load order ;

Front 95

for the following piece of code, how does javascript load it / see it ?

Back 95

Front 96

what will be the output of the following piece of code ?

Back 96

answer is 7

the code below shows how javascrip loads the code

Front 97

Name a component of javascript which never gets hoisted

Back 97

funxn expressions

Front 98

what will be the output?

Back 98

ans is 12

Front 99

what will be the output ?

Back 99

ans - error

Front 100

what will be the output when capacity status(60, 60) is called ( ignore my syntax in this qxn) ?

Back 100

error

Front 101

how can you correct the following piece of info so that , there is no error ?

Back 101

Front 102

what are the 2 ways of referencing an object property ?

Back 102

dot notation and using square brackets (obj["property1"])

Front 103

what will be the output of the following ?

Back 103

error

if u are using dot notation, u cant use dot and " "

Front 104

for the following piece of code how can you print out the destinations using a for loop --

Back 104

Front 105

what will be the output when --

return( delete obj1.prop1)

Back 105

true

Front 106

what will be the output when --

return( delete obj1.prop2)

[Note: obj1 doesnt have a prop2 ]

Back 106

true

Front 107

example of deleting a funxn property

Back 107

delete object.property1;

Front 108

can you calculate the length of an object like in array.length ?

Back 108

no - object.length will return undefined

Front 109

how to loop thru an object ? give a simple example

Back 109

Front 110

how to determine the number of fish in an aquarium object ? put this function inside the object itself.

Back 110

Front 111

what is an object's parent called ? Name 6 or 7 methods that any object inherits from it's prototype

Back 111

object prototype

Front 112

what is inheritance ?

Back 112

inheritance is the concept when objects or arrays inherit properties or methods inherit from parent variables

Front 113

from where/whom does array objects inherit its properties from ?

Back 113

the Array prototype

Front 114

from where/whom the string inherit from ? numbers inherit from ? funxns inherit from ?

Back 114

string prototype

number prototype

funxn prototype

Front 115

who is the mother or father of all prototypes ?

Back 115

object prototype

Front 116

how to create a prototype method ? what is it's use ?

Back 116

for example , u had 10 string sentence variables and u wanted to count the nmbr of a's in all of them - you can create a method for the String prototype and then make all the string sentence variables inherit from them , instead of creating separate funxns for each of them;

Front 117

how to create objects using object.create() ?

Back 117

Front 118

examples of using isPrototypeOf()

Back 118

Front 119

what is a class ?

Back 119

a class wud be a collection of similar type of objects

Front 120

x=4;

y="4";

console.log(x.valueOf());

console.log(y.valueOf());

console.log(x.valueOf()==y.valueOf());

console.log(x.valueOf()===y.valueOf());

Back 120

4

"4"

true(type coercion takes place)

false ( no type coercion takes place )