3)What is BOM?
BOM stands for Browser Object Model. It provides interaction with the browser. The default object of browser is window.
4) What is DOM? What is the use of document object?
DOM stands for Document Object Model. A document object represent the html document. It can be used to access and change the content of html.
5) What is the use of window object?
The window object is automatically created by the browser that represents a window of a browser.
It is used to display the popup dialog box such as alert dialog box, confirm dialog box, input dialog box etc.
6) What is the difference between == and ===?
The == operator checks equality only whereas === checks equality and data type i.e. value must be of same type.
7) What does the isNaN() function?
The isNan() function returns true if the variable value is not a number.
10) What are undeclared and undefined variables?
Undeclared variables are those that do not exist in a program and are not declared. If the program tries to read the value of an undeclared variable, then a runtime error is encountered.
Undefined variables are those that are declared in the program but have not been given any value. If the program tries to read the value of an undefined variable, an undefined value is returned.