undefined - JavaScript | MDN
The undefined global property represents the primitive value undefined. It is one of JavaScript's primitive types.| MDN Web Docs
The undefined global property represents the primitive value undefined. It is one of JavaScript's primitive types.| MDN Web Docs
The JSON.stringify() static method converts a JavaScript value to a JSON string, optionally replacing values if a replacer function is specified or optionally including only the specified properties if a replacer array is specified.| MDN Web Docs
The read-only scrollX property of the Window interface returns the number of pixels by which the document is currently scrolled horizontally. This value is subpixel precise in modern browsers, meaning that it isn't necessarily a whole number. You can get the number of pixels the document is scrolled vertically from the scrollY property.| MDN Web Docs
The getClientRects() method of the Element interface returns a collection of DOMRect objects that indicate the bounding rectangles for each CSS border box in a client.| MDN Web Docs
The Element.getBoundingClientRect() method returns a DOMRect object providing information about the size of an element and its position relative to the viewport.| MDN Web Docs
