The two methods should be returned according to W3C specifications. Let's take a look at the official explanation first, and then choose to use them according to W3C specifications:
QuerySelector:
Return the first matching Element node within the node's subtrees. if there is no such node, the method must return null. (return the first child tree of the specified element node that matches the selector set. If no child tree matches the selector, return null)
QuerySelectorAll:
Return a NodeList containing all of the matching Element nodes within the node's subtrees, in document order. if there are no such nodes, the method must return an empty NodeList. (return the node set that matches the selector in the subtree of the specified element node, which adopts the depth-first pre-query. If no match exists, this method returns an empty set)
Usage:
The Code is as follows:
Var element = baseElement. querySelector (selectors );
Var elementList = baseElement. querySelectorAll (selectors );
When BaseElement is document, there is no problem. The implementations of various browsers are basically the same. However, when BaseElement is a common dom Node (dom Node that supports these two methods), it is a bit strange to implement the browser. For example:
The Code is as follows:
Test
