A native JavaScript port of the jQuery isOnScreen plugin, originally created by moagrius. This plugin determines if an element is within the viewport, with optional parameters that allow the user to specify a minimum percentage of the element's dimensions that must be visible to qualify.
@param x - Float values to test against, as a decimal value of how much of the element's width must be visible for the method to return true. Defaults to 1 (100%)
@param y - Float values to test against, as a decimal value of how much of the element's height must be visible for the method to return true. Defaults to 1 (100%)
For example, passing element.isOnScreen(0.5, 0.5) would return true if the element has at least 50% of its height and width within the viewport. element.isOnScreen(0.1, 0.5) would return true if at least 10% of the width is visible and 50% of the height is visible. Omitting an argument (or passing null) defaults to 1 (or 100%).
element.isOnScreen(); // returns true if element is entirely within the viewport
element.isOnScreen(0.5, 0.5); // returns true if element is at least 50% within the viewport
TBA