How to access nodes in JavaScript

Methods to access nodes: 1. Use the ownerDocument attribute; 2. Use the parentNode attribute; 3. Use the childNodes attribute; 4. Use the firstChild attribute; 5. Use the lastChild attribute; 6. Use the nextSibling attribute, etc.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

Through the tree relationship between nodes, we can locate each node in the document. DOM defines the following properties for the Node type to facilitate JavaScript traversal of each node in the document tree.

• ownerDocument: Returns the root element (document object) of the current node
• parentNode: Returns the parent node of the current node. All nodes have only one parent node
• childNodes: Returns the node list of all child nodes of the current node
• firstChild: Returns the first child node of the current node
• lastChild: Return the last child node of the current node
• nextSibling: Return the adjacent sibling nodes after the current node
• previousSibling: Return the adjacent sibling nodes before the current node

[1]childNodes

Each node has a childNodes attribute, which stores a nodeList object, which represents a list of all child nodes.

nodeList is an array-like object used to save an ordered set of nodes. Users can access these nodes through subscript positions. Although childNodes can access the value of nodeList through square bracket syntax, and the childNodes object contains a length property, which indicates the number (length) of child nodes contained in the list, childNodes is not an array and cannot directly call array methods.

【2】parentNode

Each node has a parentNode attribute, which points to the parent node in the document tree. All nodes contained in the childNodes list have the same parent node, so their parentNode properties all point to the same node.

The node returned by the parentNode property is always an element type node, because only element nodes may contain child nodes. However, the document node has no parent node, and the parentNode property of the document node will return null.

【3】firstChild and lastChild

The firstChild property returns the first child node, and the lastChild property returns the last child node. The firstChild and lastChild properties of text nodes and attribute nodes always return null.

Note: firstChild is equivalent to the first element of childNodes, and the lastChild attribute value is equivalent to the last element of childNodes.

node.childNodes[0] = node.firstChild
node.childNodes[node.childNodes.length-1]  = node.lastChild

【4】nextSibling and previousSibling

nextSibling property returns the next adjacent node, and previousSibling property returns the previous adjacent node. If there are no adjacent nodes that share the same parent, they will return null.

【5】ownerDocument

In the DOM document tree, you can use the ownerDocument attribute to access the root node.

node.ownerDocument

Through the ownerDocument attribute of each node, we can directly access the document node without having to go through layers of backtracking to get to the top. In addition, users can also use the following methods to access the root node.

document.documentElement

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