Java Script Interview Questions and Answers

The script element can directly be added inside the body of the page. It should start with the tag <script> and end with </script> tag. The script can also be added to the head tag of the web page. Similarly the other way is by placing the script in a separate file which gets downloaded on the client's machine when the page is requested.
Embedded
<SCRIPT LANGUAGE='JavaScript Version'> JavaScript statements </SCRIPT>
Stored externally
<SCRIPT src='abc.js' />

Each elements of JavaScript can be accessed by their names. To access the page, document element is used and to access the browser the window element is used in the script. This element's values are required for several computing reason say validation check. 
For example:
var myID = windows.document.formLogin.userID.value;

Browser version incompatibility is the biggest problem. It requires knowing how each scriptable browser version implements its object model. You see, the incompatibility rarely has to do with the core JavaScript language (although there have been improvements to the language over time); the bulk of incompatibility issues have to do with the object models that each browser version implements.
The second biggest can of worms is scripting connections between multiple windows. A lot of scripter's like to have little windows pop up with navigation bars or some such gizmos. But the object models, especially in the older browser versions, don't make it easy to work with these windows the minute you put a user in front of them--users who can manually close windows or change their stacking order.

Use document.forms[0].submit();
0 refers to the index of the form's. if you have more than one form in a page, then the first one has the index 0, second has index 1 and so on. 

We can declare an array like this 
var scripts = new Array(); 
We can add elements to this array like this

scripts[0] = 'PHP';
scripts[1] = 'ASP';
scripts[2] = 'JavaScript';
scripts[3] = 'HTML';
We also can create an array like this 
var no_array = new Array(21, 22, 23, 24, 25);

An alert box displays only one button which is the OK button whereas the Confirm box displays two buttons namely OK and cancel. 
Alert ('Warning: Please enter an integer between 0 and 100.');
Confirm ('Do you really want to launch the missile?'); 

A prompt box allows the user to enter input by providing a text box. 
Prompt ('What is your temperature?');

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

You can use the parseInt() and parseFloat() methods. Notice that extra letters following a valid number are ignored. 
parseInt('100') ==> 100

You can append the number with an empty string 
var mystring = ' '+myinteger; 
or 
var mystring = myinteger.toString();

Determining the state of a checkbox in JavaScript var checkedP = window.document.getElementById('myCheckBox').checked;