Expert JavaScript Developer

By default, the parsing of the HTML code, during page loading, is paused until the script has not stopped executing. It means, if the server is slow or the script is particularly heavy, then the webpage is displayed with a delay. While using Deferred, scripts delays execution of the script till the time HTML parser is running. This reduces the loading time of web pages and they get displayed faster.

The window.onload method occurs after all the page elements have loaded(HTML, CSS, images), which can result in a delay.

The $(document).ready() method begins to run code as soon as the Document Object Model (DOM) is loaded, which should be faster and less prone to loading errors across different browsers.

► Math object has two constant : Math.PI and Math.E

► Math object has following functions :

Math.abs(val1); :It will give absolute value of val1.

Math.max(val1,val2); :This fuction will return maximum value from val1 and val2.

Math.random(); :This function will return a random number between 0 and 1.

Math.floor(val1) :This function will returns decimal value of val1.

This is one of those general open-ended questions interviewers love to throw out. The only correct answer here is one that shows you're familiar with and have an opinion on the various JavaScript libraries. You could discuss the pros and cons of using raw JavaScript vs. jQuery, or describe an instance in which you'd use one library over another. Visit jsdb.io for a complete rundown.

Break statement is used to come out of the current loop while the continue statement continues the current loop with a new recurrence.

JavaScript supports for loops, while loops, and do-while loops, but not foreach loops.

► Alert

► Confirm and

► Prompt

You can use inline event handlers to add a JavaScript handler to an HTML page element. The disadvantage of this technique is that it allows you to have one handler per element. There are different browsers which allow you to have dynamic handler added to the HTML page element. Example of inline event handler is given below:

<a href="ineh.htm" onlick="alert('Hello!')">Good Morning!</a>

// event handlers added by assignment (usually right after the page loads), e.g.:

document.onclick=clickHandler;

document.onkeydown=keyHandler;

► The decodeURI() function is used to decode the URI.

► Syntax :

decodeURI(uri)

Where uri is URI to be decoded

► For example :

<script>

var uri = "EmpDetails.asp?Emp=årpit&mode=edit";

document.write(encodeURI(uri) + "

");

document.write(decodeURI(uri) + "

");

</script>

► Output :

EmpDetails.asp?Emp=%C3%A5&mode=edit

EmpDetails.asp?Emp=årpit&mode=edit.

► encodeURI() function is used to encode the URI.

► This function does not encode following special characters :

' = , ? : $ @ / & # + '

► Syntax : encodeURI(uri), Where uri is URI to be encoded.

► For example :

<script>

var uri = "EmpDetails.asp?Emp=årpit&mode=edit";

document.write(encodeURI(uri) + "

");

</script>

Output :

EmpDetails.asp?Emp=%C3%A5&mode=edit.

The following code has to be inserted to achieve the desired effect:

XHTML

<script language="JavaScript" type="text/javascript" >

<!-- location.href="http://newhost/newpath/newfile.html"; //--></script>

For hiding JavaScript codes from old browsers:

Add "<!-" without the quotes in the code just after the <script> tag.

Add "//->" without the quotes in the code just before the <script> tag.

Old browsers will now treat this JavaScript code as a long HTML comment. While, a browser that supports JavaScript, will take the "<!-" and "//->" as one-line comments.

Null is used to assign an empty value to a variable and needs to be assigned manually.

Undefined values result when you declare a variable without assigning it a value. Undefined will be the default whenever you don't explicitly assign a value.

The isNaN() function is used to determine whether a value is not a number, or an illegal number. If the argument is not a number, the isNaN() function will return TRUE.

When the first character is a string, the remaining characters will be converted into a single string, rendering 123.

If the string is at the end, the initial characters will perform normal mathematical functions before converting into a string, resulting in 33.

► If you use innerHTML the content is replaced everytime.

► We cannot use like 'appending to innerHTML'.

► Even if we use += like "innerHTML = innerHTML + 'html'" then also the old content is replaced by html.

► If we use innerHTML then the entire innerHTML content is re-parsed and build into elements. Therefore it's much slower.

► The innerHTML doesn't provide validation and therefore we can potentially insert invalid and broken HTML in the document and break it.

Event bubbling transfers events contained within the child node to the parent node. It's a beneficial method because of its speediness, as it only requires the code to traverse the DOM tree one time.