[thelist] Diff algorithm in JavaScript

Simon Perry simon.perry at si-designs.co.uk
Thu Nov 27 17:49:56 CST 2003

Fernando Gomez wrote:

> In a JavaScript application I'm developing, the user is prompted if he 
> wants to save the changes he's made to the data in a (complex) data 
> entry form, before switching to another task.
> Given the complexity of the data entry form, I've just thought that it 
> would be nice to offer him a list of the differences between the 
> actual data and the original data, so that he can decide in case of 
> doubt.
> The data I'm taking about is compared not element by element of the 
> form; instead I build a long string with all the data in the form, 
> something like
>   "data line 1\ndata line 2\ndata line 3\ndata line 4\n..."
> and then compare this string with the original one.


Javascript supports hashes[1] so the approach I would take would be to 
create two hash objects to store your form data. Then iterate through 
the original hash to create a new array of data sets that have been 
added then again for those that have been removed.


Sudo code:
for (var n in myOriginalHashtable) {
    //compare old and new hashes and pop the differences into a new array

[1] http://www.crockford.com/javascript/survey.html

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