14.9 Creating a New Element
NN 6, IE 5
You want to generate a brand new
element and insert it into the body of the current page.
For IE 5 or later and Netscape 6 or later, use the W3C DOM
element-creation method of the document object.
The sole parameter is a string of the tag name for the element:
var elem = document.createElement("p");
You can now populate the element with properties and other content,
and then insert it into the document.
The tag name you supply as a parameter to the createElement(
) method can be upper- or lowercase, but
in keeping with current trends in XHTML practice, lowercase is the
preferred style. Your case choice does not influence the value
returned by the element's tagName
property, which uniformly returns values in all uppercase.
Invoking the createElement( ) method generates the
element in the browser's memory, but the element is
not yet part of the document node tree. To accomplish this task, use
one of the node tree modification methods on the
element that you want to be the parent node of the newly installed
- appendChild( newChild)
Adds the newChild node as the last child
of the element invoking the method. Returns a reference to the newly
appended child node.
- insertBefore( newChild, refNode)
Inserts the newChild in front of the
existing child node referenced by refNode.
Returns a reference to the newly inserted child node.
- replaceChild( newChild, oldChild)
Inserts the newChild in place of the
oldChild. Returns a reference to the
removed child node.
Here is a typical sequence that creates a new self-contained element,
sets various attributes, and puts it at the end of the
var elem = document.createElement("img");
elem.setAttribute("alt", "GiantCo Logo");
The previous sequence uses the setAttribute(
) method to assign values to what are
normally attribute values of the tag. You can also assign values to
the analogous properties of the element object, but the W3C DOM
recommendation prefers the setAttribute( ) method
for this purpose. Your choice is strictly based on programming style,
in that browsers recognize both syntaxes equally (and the property
assignment approach is less verbose).
You also are not required to set the attributes of the element prior
to inserting the element into the document tree. Again, this is a
programming style decision, but it is quite typical to load an object
with all its values before presenting it to the environment. In rare
instances, however, an element must become part of the document tree
for a scripted property to be accessible because it needs a layout
context for the property assignment to take effect (see Recipe
Internet Explorer (dating back to Version 4) has a supplementary
vocabulary (and mind-set) for creating elements and inserting them
into a document. The system is not node-oriented in the way the W3C
DOM is. Instead, it works with HTML as strings. Rather than
generating a new element object, simply assemble the HTML for the new
element as a string, and then insert the string in the desired place
within the document structure. The IE-only equivalent of the
img element creation sequence shown earlier is:
var elem = "<img src='images/logo.jpg' height='40' width='120' alt='GiantCo Logo'>";
The first parameter of the insertAdjacentHTML(
) method instructs the browser to insert
the new string just inside the </body> tag
of the document, while the method forces the browser to treat the
string as HTML so that the tags are treated as markup, rather than as
completely literal strings (displaying the angle brackets,
attributes, and so on).
It's quite clear that the HTML-string approach is
simpler in many respects, especially if you've been
using it to script IE that way for years. But the W3C DOM through
Level 2 does not (and likely will not) provide a convenient way to
deal with tagged content in string form. See Recipe 14.10 for one IE
convenience that has made its way to the Mozilla browser for element
14.9.4 See Also
Recipe 14.10 for generating text content of an element; Recipe 14.11
for creating a combination of element and text nodes for insertion
into a document; Recipe 14.12 for inserting an
iframe into a document.