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Traversing an HTML Table with JavaScript and DOM Interfaces
DYNAMICALLY MANIPULATING HTML ELEMENTS WITH DOM LEVEL 1

By Marcio Galli
Gecko Technology Evangelist

INTRODUCTION
    This technote is an overview of some powerful, fundamental DOM level 1.0 methods and how to use them from JavaScript. You will learn how to create, access and control, and remove HTML elements dynamically. The DOM methods presented here are not specific to HTML; they also apply to XML. The demonstrations provided here will work fine in any browser with full support for DOM level 1, such as the Mozilla browser or others based on it like the next-generation Navigator browser from Netscape. The code samples in this document also work on IE5.

    Note: The DOM methods presented here are part of the Document Object Model (Core) level 1 specification. DOM level 1 includes both methods for generic document access and manipulation (DOM 1 Core) as well as methods specific to HTML documents (DOM 1 HTML).

CONTENTS
QUICK SUMMARY OF DOM METHODS AND ATTRIBUTES USED IN THIS TECHNOTE
    method: document.getElementsByTagName(tagNameString) 
      Example: myDocumentElements=document.getElementsByTagName("body");
      What it does: Returns a list of all the elements in the document that have tag name tagNameString
      For more Information: W3C's DOM Level 1 - interface Document, interface Element

    method: item(n) 

      Example: myBody=myDocumentElements.item(0);
      What it does: From a list, returns item number n
      For more Information: W3C's DOM Level 1 - interface NodeList

    method: document.createElement(tagNameString) 

      Example: myNewPTAGnode=document.createElement("p");
      What it does: Creates and returns a new element with tag name tagNameString
      For more Information: W3C's DOM Level 1 - interface Document

    method: document.createTextNode(textString) 

      Example: myTextNode=document.createTextNode("world");
      What it does: Creates and returns a new text node with textString as its text
      For more Information: W3C's DOM Level 1 - interface Document

    method: parentElement.appendChild(newChildElement) 

      Example: myBody.appendChild(myNewPTAGnode);
      What it does: Adds newChildElement as a child element of parentElement at the end of the list
      For more Information: W3C's DOM Level 1 - interface Node

    attribute: textNode.data; 

      Example: textdata=myceltext.data;
      What it does: Returns a text string that is the content of textNode.
      For more Information: W3C's DOM Level 1 - interface CharacterData

    attribute: attributeNode.value; 

      Example: myattributevalue=myattribute.value;
      What it does: Returns a text string that is the value of attributeNode.
      For more Information: W3C's DOM Level 1 - interface Attr
STARTING WITH SAMPLE CODE - OVERVIEW OF SAMPLE1.HTML
    This technote is an introduction to the DOM through sample code. Once you are familiar with the Level 1 DOM's fundamental methods, you can continue your study using the additional information in the reference section. To get started, to try out the following HTML sample. It uses DOM level 1 methods from JavaScript to create an HTML table dynamically. See below for a fully commented version of this code sample. Basically, it creates a small table with four cells and text content inside each cell. The text content of the cell is: "cell is row y column x" showing the row and column numbers for that cell in the table. 

    <html>
<head>
<title>Sample code - Traversing an HTML Table with JavaScript and DOM Interfaces</title>
<script>
    function start() {
        var mybody=document.getElementsByTagName("body").item(0);
        mytable = document.createElement("TABLE");
        mytablebody = document.createElement("TBODY");
        for(j=0;j<2;j++) {
            mycurrent_row=document.createElement("TR");
            for(i=0;i<2;i++) {
                mycurrent_cell=document.createElement("TD");
                currenttext=document.createTextNode("cell is row "+j+", column "+i);
                mycurrent_cell.appendChild(currenttext);
                mycurrent_row.appendChild(mycurrent_cell);
            }
            mytablebody.appendChild(mycurrent_row);
        }
        mytable.appendChild(mytablebody);
        mybody.appendChild(mytable);
        mytable.setAttribute("border","2");
    }
</script>
</head>
<body onload="start()">
</body>
</html>

    Sample1.html - creates an example HTML Table with 4 cells, source code: sample1.html.txt

    Study carefully 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>
<tr><td>cell is row 0 column 0</td><td>cell is row 0 column 1</td></tr>
<tr><td>cell is row 1 column 0</td><td>cell is row 1 column 1</td></tr>
</TABLE>
...

    The HTML table markup thatwas dynamically generated

    Here's the DOM object tree generated by the code for the TABLE element and its child elements:


    Figure 1 - Object tree for the sample HTML Table

    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.

FUNDAMENTAL DOM METHODS - SAMPLE2.HTML
    Accessing node elements by using getElementsByTagName(..) and the item(..) methods

    Using getElementsByTagName to retrieve elements by their tag name

    getElementByTagName is a method of both the Document interface and the Element interface, so both the root document object as well as all Element objects have the getElementByTagName method. To get a list of children of some element, selecting them by tag names, you can use element.getElementsByTagName(tagname).

    getElementsByTagName returns a list of child elements that have the specified tagname. From that list of child elements, you can reach an individual element by calling the item method, passing an index for the item number you want returned. The first child element of the list is element number zero. It's easy and very simple but needs attention when you are working with large structures. In the next topic we continue working with the Table sample. The following sample is a simpler one, intended to show some basic methods: 

    <html>
<head>
<title>Sample code - Traversing an HTML Table with JavaScript and DOM
Interfaces</title>
<script>
    function start() {
        // get a list of all the body elements (there will only be one)
        myDocumentElements=document.getElementsByTagName("body");
        // the body
        element itself is the first item of the list
        myBody=myDocumentElements.item(0);
        // now, get all the p elements that are children of the body
        myBodyElements=myBody.getElementsByTagName("p");
        // get the second item of the list of p elements
        myP=myBodyElements.item(1);
    }
</script>
</head>
<body onload="start()">
<p>hi</p>
<p>hello</p>
</body>
</html>

    sample2.html. Obtaining the reference for the second P element - source code: sample2.html.txt

    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);

    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

    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.

    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);

    sample2a.html that is sample2.html with new text node child, source code: sample2a.html.txt

    Click here to see the complete source of sample2, including these two new lines to create a text node that appends itself as child of the second P element. 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.

    NOTE: 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. Click here to see an example with insertBefore and here for its source code.

    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);

    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);

    Click here to see the sample2b.html - this final example and here for the source code. The final state for the modified object tree looks like this:


SAMPLE1.HTML - CREATING A TABLE DYNAMICALLY
    For the rest of this technote we will continue working with sample1.html. The following figure shows the table object tree structure for the table created in the sample.

    Reviewing the HTML Table structure

    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.

    NOTE: 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>
<title>Sample 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;j<2;j++) {
            // creates an element whose tag name is TR
            mycurrent_row=document.createElement("TR");
            for(i=0;i<2;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>

MANIPULATING THE TABLE WITH DOM AND CSS
    Getting a text node from a 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.

    NOTE: 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);

    sample1a.html - sample1 example with additional DOM tests - source code: sample1a.html.txt

    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 get attributes, use the getAttribute method, which returns an attribute object. To retrieve the value of the attribute, use the value property: 

    myattribute=mytable.getAttribute("boder");
myattributevalue=myattribute.value;
alert("myattributevalue");

    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;j<2;j++) {
           mycurrent_row=document.createElement("TR");
           for(i=0;i<2;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>

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