Uploading and Working with Files
The ability to allow users to upload files is a very important feature in modern web design. SharePoint provides out-of-the-box file upload capability, but the out-of-the-box file upload control is embedded in a SharePoint page without providing any extensibility to this feature. There are times when business logic requires us to provide users with file upload capability without ever leaving the page (e.g., when filling out a form) or to provide a different user interface or file preview capability. In such advanced scenarios for working with files, we need to allow users to upload files to SharePoint from the client side.