JS, CSS, HTML Interview Questions Flashcards by Steve Behm

What is JavaScript?

JS is a client-side(front-end) and server-side(back-end) scripting language

JS is an OOP language

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Enumerate the differences between Java and JavaScript

As far as I know Java is to JavaScript as pool is to pool table

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What are the JS data-types?

object
number
string
boolean
null
undefined
symbol

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What is the use of the NaN function?

Checks to see if a something is a number and returns a boolean value

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Which is faster, JS or an ASP script?

JS will be faster if you compare its client-side aspect to the ASP since it is server-side and will run slower

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What is negative infinity?

the largest negative number possible

it can be derived by dividing any negative number by 0

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Is it possible to break JS code into several lines?

Yes you can use an \n at the end of a line to create a break

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Which company developed JS?

Netscape by Brendan Eich

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What are undeclared and undefined variables?

Undeclared: undeclared variables are those that do not exist in the code

Undefined: variables that have been declared but not given a value yet

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What are global variables? How are these variables declared?

Global variables are declared with the var keyword and are accessible anywhere in the code
meaning they are without scope.

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What is a prompt box?

A prompt box is a box that allows the user to enter input by providing a text box

A label and box will be provided to enter data into

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What is the ‘this’ keyword in JS?

“this” refers to the object from where it was called

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What is the working of timers in JS?

Timers are used to execute a specific piece of code at a set time or to repeat on a specific interval

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Which symbol is used for comments in JavaScript?

/* for multi-line comments */

// for single line comments

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What is the difference between ViewState and SessionState?

‘ViewState’ is specific to a page in session

SessionState is specific to user-specific data that can be accessed across all web application pages

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What is the === operator?

Strictly equals and it looks at whether two pieces of data are identical in type and value

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How can you submit a form in JS?

document.form[0].submit()

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Does JS support automatic type conversion?

yes, JS does support automatic type conversion

truthy and falsy values are good examples of this in practice

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How can the style/class of an element be changed?

get the element from the DOM and either change the style property or change the className property

How to read and write a file using JS?

Using JS extensions

Using a web page and Active X objects

What are all the looping structures in JS?

For loop
while loop
for in loop
Do while loops

What is Variable typing in JS?

it means JS will figure out what type of data you have and make the necessary adjustments so you don’t have to redefine your different types of data

It does this through type conversion

How can you convert the string of any base to an integer in JS?

The parseInt() function is used to convert numbers between different bases.

What is the difference between == and ===?

== is not strict equality and so it allows for type conversion to take place unlike string equality with ===

== only checks for value
=== checks value and data type

What would be the result of 3 + 2 + "7"?

How to detect the operating system on the client machine?

In order to detect the operating system on the client machine, the navigator. Platform string (property) should be used.

What do you mean by NULL in JS?

The NULL value is used to represent nothing. However, it is often the case where null is assigned as a value to something that's value will change later. It can act almost like a empty parking lot.

What is the function of the delete operator?

The delete operator is used to delete the the property and the value of an object

What is JSON?

JavaScript Object Notation standard text based format that is used to represent structured data based on JS object syntax. Commonly used to send data between a client and a sever

What is the undefined value in JS?

undefined is also nothing and it can mean multiple things as it is thought of more as a the program telling you the value of something is nothing variable doesn't exist variable has no value property doesn't exist etc etc

What are all the types of pop-up boxes in JS?

alert confirm and prompt

What is the use of Void(0)?

it is used to prevent the page from refreshing used to call another method without refreshing the page

What is the data type of variables in JS?

all variables are objects

What is the difference between an alert box and a confirmation box?

an alert box displays only one button "ok" a confirmation box displays two buttons "ok" and "cancel"

What are escape characters?

Escape characters or backslashes are used when working with special characters like single quotes, double quotes, apostrophes, and ampersands. Place the backslash before the characters to make it display

What are JS cookies?

Cookies are the small test files stored in a computer, and they get created when the user visits the websites to store information they need. Examples could be username details and shopping cart info from previous visits.

What does pop() method do in JS?

The pop method will remove the last element from an array and returns the removed element.

Does JS have concept level scope?

No. A variable declared inside the function has scope inside the function

What are the disadvantages to using innerHTML in JS?

Content is replaced everywhere | It poses a security risk as well

What are break and continue statements?

Break: exits from the current loop Continue: continues to the next statement in the loop

What are the 2 basic data types in JS?

Primitives Reference types (array, function, object)

How can generic objects be created in JS?

since js is not strictly a typed language we don't need to write generic objects

What is the use of a type operator?

typeof is an operator used to return a string description of the type of a variable

Which keywords are used to handle exceptions?

Try Catch Finally

Which keyword is used to print the text on the screen?

Document.Write("word") is used to print the text "word" on the screen.