All Javascripts have access to a built-in object called document. The document object allows you to manipulate the current web page by accessing document properties and functions. For example,
document.write("Hello"); adds the text Hello to the browser window.

There are additional built-in objects that Javascript programmers can use. The Math object is another object to which all Javascript programmers have access.

Math has a property named PI and a property named E that have the approximate values of pi and e stored in them. Therefore, the statement
document.write(Math.PI, " is pi and e is ", Math.E); would display 3.141592653589793 is pi and e is 2.718281828459045 Below is a summary of the functionality available through the use of the Math object. 

Function                      Purpose
Math.abs(num) returns the absolute value of num Math.sin(angle) returns the sin, cos, or tan of angle, Math.cos(angle) where angle is a radian measure Math.tan(angle) Math.acos(value) returns the angle (in radians) for the value Math.asin(value) as calculated by the corresponding inverse trig function Math.atan(value) Math.exp(num) returns E to the num power and the natural Math.log(num) log of num, respectively Math.ceil(num) returns the smallest integer bigger than or equal to num Math.floor(num) returns the largest integer less than or equal to num Math.min(num1, num2) returns the smaller of num1 and num2 Math.max(num1, num2) returns the larger of num1 and num2 Math.pow(b, x) returns b to the x power Math.round(num) returns the integer closest to num Math.sqrt(num) returns the square root of num