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What is the difference between undefined value and null value?
JavaScript Interview Questions and Answers
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68. What is the difference between undefined value and null value?
(i)Undefined value cannot be explicitly stated that is there is no keyword called undefined whereas null value has keyword called null
(ii)typeof undefined variable or property returns undefined whereas
typeof null value returns object
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Other Interview Questions
- What is JavaScript?
- How is JavaScript different from Java?
- What’s relationship between JavaScript and ECMAScript?
- How do you submit a form using Javascript?
- How do we get JavaScript onto a web page?
- How to read and write a file using javascript?
- How to detect the operating system on the client machine?
- How can JavaScript make a Web site easier to use? That is, are there certain JavaScript techniques that make it easier for people to use a Web site?
- How can JavaScript be used to improve the "look and feel" of a Web site? By the same token, how can JavaScript be used to improve the user interface?
- What are JavaScript types?
- How do you convert numbers between different bases in JavaScript?
- How to create arrays in JavaScript?
- How do you target a specific frame from a hyperlink?
- What is a fixed-width table and its advantages?
- Example of using Regular Expressions for syntax checking in JavaScript
- How to add Buttons in JavaScript?
- Where are cookies actually stored on the hard disk?
- What can javascript programs do?
- How to set a HTML document's background color?
- How can JavaScript be used to personalize or tailor a Web site to fit individual users?
- Are you concerned that older browsers don't support JavaScript and thus exclude a set of Web users? individual users?
- What does isNaN function do?
- What is negative infinity?
- In a pop-up browser window, how do you refer to the main browser window that opened it?
- What is the data type of variables of in JavaScript?
- Methods GET and POST in HTML forms - what's the difference?.
- How to write a script for "Select" lists using javascript
- Text From Your Clipboard?
- What does the "Access is Denied" IE error mean?
- Is a javascript script faster than an ASP script?
- Are Java and JavaScript the Same?
- How to embed javascript in a web page?
- What and where are the best JavaScript resources on the Web?
- What are the problems associated with using JavaScript, and are there JavaScript techniques that you discourage?
- What boolean operators does JavaScript support?
- What does "1"+2+4 evaluate to?
- What are the ways to emit client-side JavaScript from server-side code in ASP.NET?
- What is the difference between RegisterClientScriptBlock and RegisterStartupScript?
- What is the difference between a web-garden and a web-farm?
- How to get the contents of an input box using Javascript?
- How to determine the state of a checkbox using Javascript?
- How to set the focus in an element using Javascript?
- How to access an external javascript file that is stored externally and not embedded?
- What is the difference between an alert box and a confirmation box?
- What is a prompt box?
- Can javascript code be broken in different lines?
- Taking a developer’s perspective, do you think that that JavaScript is easy to learn and use?
- What Web sites do you feel use JavaScript most effectively (i.e., best-in-class examples)? The worst?
- How about 2+5+"8"?
- What is the difference between SessionState and ViewState?
- What does the EnableViewStateMac setting in an aspx page do?
- How to Accessing Elements using javascript?
- What looping structures are there in JavaScript?
- To put a "close window" link on a page ?
- How to hide javascript code from old browsers that dont run it?
- How to comment javascript code?
- Name the numeric constants representing max,min values
- What does javascript null mean?
- How do you create a new object in JavaScript?
- How do you assign object properties?
- What’s a way to append a value to an array?
- What is this keyword?
- What does the term sticky session mean in a web-farm scenario? Why would you use a sticky session? What is the potential disadvantage of using a sticky session?
- You have an ASP.NET web application running on a web-farm that does not use sticky sessions - so the requests for a session are not guaranteed to be served the same machine. Occasionally, the users get error message Validation of viewstate MAC failed. What could be one reason that is causing this error?
- To set all checkboxes to true using JavaScript?
- How to select an element by id and swapping an image ?
- What does undefined value mean in javascript?
- What is the difference between undefined value and null value?
- What is variable typing in javascript?
- Does javascript have the concept level scope?
- What are undefined and undeclared variables?
- What is === operator ?
- How to find the selected radio button immediately using the 'this' variable?
- How to find radio button selection when a form is submitted?
- How to disable an HTML object
- To write messages to the screen without using "document.write()" ?
- How to Add new elements dynamically.
- how to have an element invoke a javascript on selection, instead of going to a new URL:
- How to have the status line update when the mouse goes over a link (The support of the status line is sporadic)?
- How to create a popup warning box
- How to create a confirmation box?
- How to create an input box?
- How to open a window with no toolbar, but with the location object.
- How to setting a cookie with the contents of a textbox ?
- How to getting values from cookies to set widgets?
- How to Handle Event Handlers?
- How to remove the event listener:
- How to change style on an element?
- How to make elements invisible
- How to set the cursor to wait.
- How to reload the current page
- how to force a page to go to another page using JavaScript?
- How to convert a string to a number using JavaScript?
- How to convert numbers to strings using JavaScript?
- How to test for bad numbers using JavaScript?
- What's Math Constants and Functions using JavaScript?
- What's the Date object using JavaScript?
- What does the delete operator do?
- How tp create Arrays using JavaScript??
- How to delete an entry using JavaScript?
- How to use strings as array indexes using JavaScript?
- How to use "join()" to create a string from an array using JavaScript?
- How to make a array as a stack using JavaScript?
- How to shift and unshift using JavaScript?
- How to create an object using JavaScript?
- How to associate functions with objects using JavaScript?
- eval()?
- What does break and continue statements do?
- How to create a function using function constructor?
- What's Prototypes for JavaScript?
- unescape(), escape()
- decodeURI(), encodeURI()
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