How to Check if the Variable is Undefined
This tutorial provides the method of checking whether the type of the variable is undefined. Read about the differences between undefined and “undefined”.
How to Check if User Has Scrolled to the Bottom of the Page
Read this tutorial and learn information about jQuery method that is run for checking whether the user has scrolled to the bottom of the page or near to it.
How to Check Whether an Object is a Date
How to Clear the Canvas for Redrawing
How to Compare Two JavaScrpt Arrays
You can either loop through the arrays or convert them to string and then compare. This tutorial provides several fast methods of comparing two arrays.