使用Javascript和DOM Interfaces来处理HTML
2016-02-19 12:03
给自己一点时间接受自己,爱自己，趁着下午茶的时间来学习图老师推荐的使用Javascript和DOM Interfaces来处理HTML，过去的都会过去，迎接崭新的开始，释放更美好的自己。
Note the order in which we created the elements and the text node:
First we created the TABLE element.
Next, we created the TBODY element, which is a child of the TABLE element.
Next, we used a loop to create the TR elements, which are children of the TBODY element.
For each TR element, we used a loop to create the TD elements, which are children of TR elements.
For each TD element, we then created the text node with the table cell's text.
Once we have created the TABLE, TBODY, TR, and TD elements and then the text node, we then append each object to its parent in the opposite order:
First, we attach each text node to its parent TD element using
mycurrent_cell.appendChild(currenttext);
Next, we attach each TD element to its parent TR element using
mycurrent_row.appendChild(mycurrent_cell);
Next, we attach each TR element to the parent TBODY element using
mytablebody.appendChild(mycurrent_row);
Next, we attach the TBODY element to its parent TABLE element using
mytable.appendChild(mytablebody);
Next, we attach the TABLE element to its parent BODY element using
mybody.appendChild(mytable);
Remember this technique. You will use it frequently in programming for the W3C DOM. First, you create elements from the top down; then you attach the children to the parents from the bottom up.
Here's the HTML markup generated by the JavaScript code:
...
TABLE border=5
trtdcell is row 0 column 0/tdtdcell is row 0 column 1/td/tr
trtdcell is row 1 column 0/tdtdcell is row 1 column 1/td/tr
/TABLE
...
Here's the DOM object tree generated by the code for the TABLE element and its child elements:
Image:sample1-tabledom.jpg
You can build this table and its internal child elements by using just a few DOM methods. Remember to keep in mind the tree model for the structures you are planning to create; this will make it easier to write the necessary code. In the TABLE tree of Figure 1 the element TABLE has one child, the element TBODY. TBODY has two children. Each TBODY's child (TR) has one child (TD). Finally, each TD has one child, a text node.
2、
In this example, we set the myP variable to the DOM object for the second p element inside the body:
First, we get a list of all the body elements via
document.getElementsByTagName("body")
Since there is only one body element in any valid HTML document, this list will have only one item.
Next, we get the first element on that list, which will be the object for the body element itself, via
myBody=myDocumentElements.item(0);
Next, we get all the p elements that are children of the body via
myBodyElements=myBody.getElementsByTagName("p");
Finally, we get the second item from the list of p elements via
myP=myBodyElements.item(1);
Image:sample2a2.jpg
Once you have gotten the DOM object for an HTML element, you can set its properties. For example, if you want to set the style background color property, you just add:
myP.style.background="rgb(255,0,0)";
// setting inline STYLE attribute
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Creating TextNodes with document.createTextNode(..)
Use the document object to invoke the createTextNode method and create your text node. You just need to pass the text content. The return value is an object that represents the text node.
myTextNode=document.createTextNode("world");
This means that you have created a node of the type TEXT_NODE (a piece of text) whose text data is "world", and myTextNode is your reference to this node object. To insert this text into your HTML page, you need to make this text node a child of some other node element.
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Inserting Elements with appendChild(..)
So, by calling myP.appendChild([node_element]), you are making the element a new child of the second P element.
myP.appendChild(myTextNode);
After testing this sample, note that the words hello and world are together: helloworld. So visually, when you see the HTML page it seems like the two text nodes hello and world are a single node, but remember that in the document model, there are two nodes. The second node is a new node of type TEXT_NODE, and it is the second child of the second P tag. The following figure shows the recently created Text Node object inside the document tree.
Image:sample2b2.jpg
createTextNode and appendChild is a simple way to include white space between the words hello and world. Another important note is that the appendChild method will append the child after the last child, just like the word world has been added after the word hello. So if you want to append a Text Node between hello and world you will need to use insertBefore instead of appendChild.
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Creating New Elements with the document object and the createElement(..) method
You can create new HTML elements or any other element you want with createElement. For example, if you want to create a new P element as a child of the BODY element, you can use the myBody in the previous example and append a new element node. To create a node simply call document.createElement("tagname"). For example:
myNewPTAGnode=document.createElement("p");
myBody.appendChild(myNewPTAGnode);
Image:sample2c.jpg
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Removing nodes with the removeChild(..) method
Each node can be removed. The following line removes the text node which contains the word world of the myP (second P element).
myP.removeChild(myTextNode);
Finally you can add myTextNode (which contains the word world) into the recently created P element:
myNewPTAGnode.appendChild(myTextNode);
The final state for the modified object tree looks like this:
Image:sample2d.jpg
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Creating a table dynamically (back to Sample1.html)
For the rest of this article we will continue working with sample1.html. The following figure shows the table object tree structure for the table created in the sample.
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Reviewing the HTML Table structure
Image:sample1-tabledom.jpg
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Creating element nodes and inserting them into the document tree
The basic steps to create the table in sample1.html are:
Get the body object (first item of the document object).
Create all the elements.
Finally, append each child according to the table structure (as in the above figure). The following source code is a commented version for the sample1.html.
At the end of the start function there is a new line of code. The table's border property was set using another DOM method, setAttribute. setAttribute has two arguments: the attribute name and the attribute value. You can set any attribute of any element using the setAttribute method.
head
titleSample code - Traversing an HTML Table with JavaScript and DOM Interfaces/title
script
function start() {
// get the reference for the body
var mybody=document.getElementsByTagName("body").item(0);
// creates an element whose tag name is TABLE
mytable = document.createElement("TABLE");
// creates an element whose tag name is TBODY
mytablebody = document.createElement("TBODY");
// creating all cells
for(j=0;j2;j++) {
// creates an element whose tag name is TR
mycurrent_row=document.createElement("TR");
for(i=0;i2;i++) {
// creates an element whose tag name is TD
mycurrent_cell=document.createElement("TD");
// creates a Text Node
currenttext=document.createTextNode("cell is row "+j+", column "+i);
// appends the Text Node we created into the cell TD
mycurrent_cell.appendChild(currenttext);
// appends the cell TD into the row TR
mycurrent_row.appendChild(mycurrent_cell);
}
// appends the row TR into TBODY
mytablebody.appendChild(mycurrent_row);
}
// appends TBODY into TABLE
mytable.appendChild(mytablebody);
// appends TABLE into BODY
mybody.appendChild(mytable);
// sets the border attribute of mytable to 2;
mytable.setAttribute("border","2");
}
/script
/head
body onload="start()"
/body
/html
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Manipulating the table with DOM and CSS
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Getting a text node from the table
This example introduces two new DOM attributes. First it uses the childNodes attribute to get the list of child nodes of mycel. The childNodes list includes all child nodes, regardless of what their name or type is. Like getElementsByTagName, it returns a list of nodes. The difference is that getElementsByTagName only returns elements of the specified tag name. Once you have the returned list, use item(x) method to retrieve the desired child item. This example stores in myceltext the text node of the second cell in the second row of the table. Then, to display the results in this example, it creates a new text node whose content is the data of myceltext and appends it as a child of the BODY element.
If your object is a text node, you can use the data attribute and retrieve the text content of the node.
mybody=document.getElementsByTagName("body").item(0);
mytable=mybody.getElementsByTagName("table").item(0);
mytablebody=mytable.getElementsByTagName("tbody").item(0);
myrow=mytablebody.getElementsByTagName("tr").item(1);
mycel=myrow.getElementsByTagName("td").item(1);
// first item element of the childNodes list of mycel
myceltext=mycel.childNodes.item(0);
// content of currenttext is the data content of myceltext
currenttext=document.createTextNode(myceltext.data);
mybody.appendChild(currenttext);
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Getting an attribute value
At the end of sample1 there is a call to setAttribute on the mytable object. This call was used to set the border property of the table. To retrieve the value of the attribute, use the getAttribute method:
mytable.getAttribute("border");
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Hiding a column by changing style properties
Once you have the object in your JavaScript variable, you can set style properties directly. The following code is a modified version of sample1.html in which each cell of the second column is hidden and each cell of the first column is changed to have a red background. Note that the style property was set directly.
html
body onload="start()"
/body
script
function start() {
var mybody=document.getElementsByTagName("body").item(0);
mytable = document.createElement("TABLE");
mytablebody = document.createElement("TBODY");
for(j=0;j2;j++) {
mycurrent_row=document.createElement("TR");
for(i=0;i2;i++) {
mycurrent_cell=document.createElement("TD");
currenttext=document.createTextNode("cell is:"+i+j);
mycurrent_cell.appendChild(currenttext);
mycurrent_row.appendChild(mycurrent_cell);
// set the cell background color
// if the column is 0. If the column is 1 hide the cel
if(i==0) {
mycurrent_cell.style.background="rgb(255,0,0)";
} else {
mycurrent_cell.style.display="none";
}
}
mytablebody.appendChild(mycurrent_row);
}
mytable.appendChild(mytablebody);
mybody.appendChild(mytable);
}
/script
/html
取自"http://developer.mozilla.org/cn/docs/%E4%BD%BF%E7%94%A8Javascript%E5%92%8CDOM_Interfaces%E6%9D%A5%E5%A4%84%E7%90%86HTML"
页面分类: DOM
