The id property of the Element interface represents the element's identifier, reflecting the id global attribute.
If the id value is not the empty string, it must be unique in a document.
The id is often used with getElementById() to retrieve a particular element. Another common case is to use an element's ID as a selector when styling the document with CSS.
Note: Identifiers are case-sensitive, but you should avoid creating IDs that differ only in the capitalization.