JavaScript Examples Bible - UserWorks Technologies

22 JavaScript Examples Bible: The Essential Companion to JavaScript Bible
Example
The following simplified function accepts a parameter that can be any object in a
document hierarchy. The script finds out the reference of the object’s containing
document for further reference to other objects:
function getCompanionFormCount(obj) {
var ownerDoc = obj.document
return ownerDoc.forms.length
}
Because the ownerDoc variable contains a valid reference to a document object, the
return statement uses that reference to return a typical property of the document
object hierarchy.
firstChild
lastChild
elementObject.firstChild
NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5
Compatibility ✓ ✓ ✓
Example
These two properties come in handy for Listing 15-10, whose job it is to either
add or replace LI elements to an existing OL element. You can enter any text you
want to appear at the beginning or end of the list. Using the firstChild and
lastChild properties simplifies access to the ends of the list. For the functions
that replace child nodes, the example uses the replaceChild() method.
Alternatively for IE4+, you can modify the innerText property of the objects
returned by the firstChild or lastChild property. This example is especially
interesting to watch when you add items to the list: The browser automatically
renumbers items to fit the current state of the list.
Listing 15-10: Using firstChild and lastChild Properties
firstChild and lastChild Properties
// helper function for prepend() and append()
function makeNewLI(txt) {
var newItem = document.createElement(“LI”)
newItem.innerHTML = txt
return newItem
}
function prepend(form) {
var newItem = makeNewLI(form.input.value)
var firstLI = document.getElementById(“myList”).firstChild
document.getElementById(“myList”).insertBefore(newItem, firstLI)