In web development, DOM (Document Object Model) is a very important concept. It allows developers to easily modify and operate the HTML or XML document of a web page, such as adding, deleting, modifying elements, etc. The built-in DOM operation library in PHP also provides developers with rich functions. This article will introduce the DOM operation guide in PHP, hoping to help everyone.

1. The basic concept of DOM

DOM is a cross-platform, language-independent API that can represent XML or HTML documents as a tree structure, in which each Nodes are all objects, and there is a parent-child relationship between objects. This tree structure allows developers to easily traverse and manipulate documents.

In DOM, each element in the web document is represented as a node. Nodes can be divided into several types such as element nodes, text nodes, comment nodes and attribute nodes. Developers can access and modify the content of nodes through the node's name, attributes, sub-nodes, etc.

2. Usage of DOM extension library

In PHP, the DOM extension library provides a set of commonly used APIs that can help developers easily manipulate and modify HTML or XML document. Some of the commonly used APIs are as follows:

(1) Create a DOM document object

Before using the DOM extension library for document operations, you must first create a DOM document object. This can be achieved through the DOMDocument class:

$doc=new DOMDocument();

(2) Reading XML or HTML documents

You can use the load() or loadHTML() method of the DOMDocument class to read XML or HTML documents, for example :

$doc->load("example.xml");

(3) Traverse document nodes

You can use the methods provided by the DOMDocument class to traverse document nodes, for example:

$root=$doc->getElementsByTagName("root")->item(0);
foreach($root->childNodes as $child){
    //處理子節(jié)點
}

(4) Add and delete nodes

You can use the methods provided by the DOMDocument class to add and delete nodes, for example:

//添加一個元素節(jié)點
$newElement=$doc->createElement("newElement");
$root->appendChild($newElement);

//刪除一個元素節(jié)點
$oldElement=$doc->getElementsByTagName("oldElement")->item(0);
$oldElement->parentNode->removeChild($oldElement);

(5) Find nodes

You can use the methods provided by the DOMDocument class to find nodes, for example:

//通過標簽名查找元素節(jié)點
$elements=$doc->getElementsByTagName("example");
foreach($elements as $element){
    //處理元素節(jié)點
}

//通過屬性值查找元素節(jié)點
$elements=$doc->getElementsByAttribute("id","exampleId");
foreach($elements as $element){
    //處理元素節(jié)點
}

(6) Modify node content

You can use the methods provided by the DOMElement class to modify the node content, for example:

//修改元素節(jié)點的文本內(nèi)容
$element=$doc->getElementsByTagName("example")->item(0);
$element->textContent="new text";

//修改元素節(jié)點的屬性值
$element=$doc->getElementsByTagName("example")->item(0);
$element->setAttribute("attrName","attrValue");

3. Practical combat of DOM operations

Here, we will introduce some practical DOM operations so that developers can better understand the application of DOM operations.

(1) Replace an element node

In the following example, we will use DOM operations to replace an element node with another new element node:

$doc=new DOMDocument();
$doc->load("example.xml");
$root=$doc->getElementsByTagName("root")->item(0);
$newElement=$doc->createElement("newElement");
$oldElement=$doc->getElementsByTagName("oldElement")->item(0);
$root->replaceChild($newElement,$oldElement);

(2) Find an element node

In the following example, we will use DOM operations to find an element node with a specified name:

$doc=new DOMDocument();
$doc->load("example.xml");
$elements=$doc->getElementsByTagName("example");
foreach($elements as $element){
    //處理元素節(jié)點
}

(3) Add an element node

In the following example, we will use DOM operations to add a new element node to the specified position:

$doc=new DOMDocument();
$doc->load("example.xml");
$root=$doc->getElementsByTagName("root")->item(0);
$newElement=$doc->createElement("newElement");
$insertBefore=$doc->getElementsByTagName("insertBefore")->item(0);
$root->insertBefore($newElement,$insertBefore);

4. Summary

This article introduces PHP DOM operation guide, including the concept of DOM, the use of DOM API and practical applications. The powerful functions of DOM can help developers easily modify and operate HTML or XML documents and improve development efficiency, which is very valuable for web developers. I hope this article can help developers who need to learn DOM operations.

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