The prompt box is used to get input from the user. It has an inbuilt text box where the user can type a value. After typing the data, the user must click on either 'OK' or cancel to continue. The value entered by the user is stored in a variable and the further action can be taken.

if a web document contains a form element it can be referred in JavaScript using the syntax -document.forms[0]

If the Web document contains two form elements the first form is referred to as document.forms[0] and the second document.forms[1]. Therefore we can access first form element using document.forms[0].elements[0], the second element can be accessed as document.forms[0].elements[1] and so on.

The onerror event triggers when an image does not load properly. It can be written as onerror="error handling code"

Path is not a valid property of the 'plugin' object.

The ceil method rounds a number upward to it's nearest integer. The result of ceil(5.3) will be 6

The appName property returns the name of the browser for example Microsoft Internet Explorer or FireFox.

'policy' is not a valid cookie field.

The href property of the 'Location' object returns the entire path or URL of the current page.

The indexOf() returns the index or position of a character or a string in the given string. The indexOf() returns -1 is the searched character is not found. For example in the following codevar str="aliensbrain.com"; var n=str.indexOf("l");The value of 'n' will be '2' since it is the 2nd character in the string starting from 0.

Multithreading is the process of running multiple threads simultaneously. JavaScript doesn't have any multithreading or multiprocess capabilities.

The W meta character is used to find a non-word character.'W' searches any character that is not a word character from the basic Latin alphabet. Equivalent to [^A-Za-z0-9_].

The 'in' operator returns true if the specified property is in the specified object. The following syntax can be used for the 'in' operator propertyname in objectname

The result will be Element 4. The other elements will not be printed. To print all the values of the array a loop can be used.

The finally block contains the code that we want to run irrespective of whether the try block contains an exception or not. If the try block has an exception the control will move from the try block to the catch block and then to the finally block. If there is no exception the control will move directly from the try block to the finally block.

The isNaN function evaluates an argument to determine if it is NaN (not a number). The syntax of isNaN is -  isNan(value_to_check);

The width and height property of the screen object returns the total width and height of the screen.

The onblur event occurs when a control on the form loses it focus. This event is mainly used for data validation purpose when the user tries to leave a control after filling the data.

Functions are another type of variable in JavaScript. Creating a function within another function changes the scope of the function in the same way it would change the scope of a variable.The functions defined within another function won't be accessible outside the function unless they have been attached to an object that is accessible outside the function. In the above code, we are calling the function named 'fun3()' , which in turn is calling another function named 'fun1()' with two arguments (5) and (5). The fun1() will copy the value of the first 5 to i and the second value will be copied to j. The result of fun2() will be sent to 'fun1()'. fun1() will return the result (25) to fun3(). The result will be copied to the variable 'r' and printed using an alert box.

'bool' is not a reserved JavaScript keyword. 

It is not compulsory to pass an argument while calling the substring() function. If no arguments are specified, the actual string will be printed as it is. In the following example, the output will be 'welcome'

var str=welcome;document.write(str.substring());

The typeof operator in JavaScript identifies null values as being of type Object, not of type boolean.

JavaScript can not directly access files on the user's system the only exception is the access to the browser's cookie files. 

String can be used as an identifier even if the strict option is specified.

The split() method is used to split a string into an array of substrings, and returns the new array. In the above code, the spaces of the string will be converted to commas (,)

Each element that we want to modify dynamically must be assigned a unique id. The InnerHTML property is used along with the getElementById() method to refer to a particular element by using its Id.