Jquery $(document).ready function event executes a bit earlier than window.onload() and called once the DOM(Document object model) is loaded on your page i.e.(anchor tag, table, div tag, paragraph tag etc..). It will not wait for the images, frames to get fully load. It means that it is the earliest stage in page load process.
ready event occurs after the HTML document has been loaded, while the
onload event occurs later, when all content (e.g. images) also has been loaded.
onload event is a standard event in the DOM, while the
ready event is specific to jQuery. The purpose of the
ready event is that it should occur as early as possible after the document has loaded, so that code that adds functionality to the elements in the page doesn’t have to wait for all content to load.