JavaScript Interview Question

There are many things that you can do ahead of time to prepare for the interviewing process, and move yourself a step above of the competition. Updating your resume and reviewing frequently asked interview questions can be very effective, and goes a long way in getting the most out of your interview.

What Web sites do you feel use JavaScript most effectively (i.e., best-in-class examples)? The worst?

The best sites are the ones that use JavaScript so transparently, that I'm not aware that there is any scripting on the page. The worst sites are those that try to impress me with how much scripting is on the page.

 

How about 2+5+"8"?

Since 2 and 5 are integers, this is number arithmetic, since 8 is a string, it's concatenation, so 78 is the result.

 

What is the difference between SessionState and ViewState?

ViewState is specific to a page in a session. Session state refers to user specific data that can be accessed across all pages in the web application.

 

What does the EnableViewStateMac setting in an aspx page do?

Setting EnableViewStateMac=true is a security measure that allows ASP.NET to ensure that the viewstate for a page has not been tampered with. If on Postback, the ASP.NET framework detects that there has been a change in the value of viewstate that was sent to the browser, it raises an error - Validation of viewstate MAC failed.
Use <%@ Page EnableViewStateMac="true"%> to set it to true (the default value, if this attribute is not specified is also true) in an aspx page.

 

How to Accessing Elements using javascript?

To do something interesting with HTML elements, we must first be able to uniquely identify which element we want. In the example
<body>
<form action="">
<input type="button" id="useless" name="mybutton" value="doNothing" />
</form>
</body>

We can use the "getElementById" method (which is generally preferred)
document.getElementById("useless").style.color = "red";
or we can use the older hierarchical navigation method,
document.forms[0].mybutton.style.color = "blue";
Notice that this uses the "name" attribute of the element to locate it.
# Example of Accessing Elements in a DOM.

<script type="text/javascript" >
function showStatus() {
var selectWidget = document.forms.beerForm.elements["beer"];
var myValue = selectWidget.options[selectWidget.selectedIndex].value;
alert('You drank a \"'+ myValue +"\"");
return true;
}
</script>

<form name="beerForm" action="">
<select name="beer">
<option selected="selected">Select Beer</option>
<option>Heineken</option>
<option>Amstel Light</option>
<option>Corona</option>
<option>Corona Light</option>
<option>Tecate</option>
</select>

<input type="button" name="submitbutton" value="Drink"
onclick="showStatus()" />
</form>

 

What looping structures are there in JavaScript?

for, while, do-while loops, but no foreach.