JavaScript Examples Bible - UserWorks Technologies

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JavaScript Examples Bible: The Essential Companion to JavaScript Bible
Listing 19-11 includes an undo buffer that accurately undoes only the changes made
in the initial replacement actions.
The undo buffer stores its data in two global variables. The first,
origSearchString, is simply the string used to perform the original search. This
variable is the string that has to be put back in the places where it had been
replaced. The second global variable is an array that stores TextRange bookmarks
(see getBookmark() later in this chapter). These references are string values that
don’t mean much to humans, but the browser can use them to recreate a range
with its desired start and end points. Values for both the global search string and
bookmark specifications are stored in calls to the pushUndoNew() method each
time text is replaced.
A perhaps unexpected action of setting the text property of a text range is that
the start and end points collapse to the end of the new text. Because the stored
bookmark must include the replaced text as part of its specification, the start point
of the current range must be adjusted back to the beginning of the replacement text
before the bookmark can be saved. Thus, the pushUndoNew() function receives the
replacement text string so that the moveStart() method can be adjusted by the
number of characters matching the length of the replacement string.
After all of the bookmarks are stored in the array, the undo action can do its job
in a rather simple for loop inside the undoReplace() function. After verifying that
the undo buffer has data stored in it, the function loops through the array of bookmarks
and replaces the bookmarked text with the old string. The benefit of using
the bookmarks rather than using the replacement function again is that only those
ranges originally affected by the search-and-replace operation are touched in the
undo operation. For example, in this document if you replace a case-sensitive
“states” with “States” two replacements are performed. At that point, however, the
document has four instances of “States,” two of which existed before. Redoing the
replacement function by inverting the search-and-replace strings would convert all
four back to the lowercase version — not the desired effect.
getBookmark()
TextRange.getBookmark()
NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5
Compatibility ✓ ✓ ✓
Example
Listing 19-11 earlier in this chapter shows how the getBookmark() method is
used to preserve specifications for text ranges so that they can be called upon
again to be used to undo changes made to the text range. The getBookmark()
method is used to save the snapshots, while the moveToBookmark() method is
used during the undo process.