Having trouble understanding how the prefilter should work

[tnrich]

I am a little bit confused by the documentation of the pre-filter functionality.

At one point in the readme, it says:
"Diff arguments:
prefilter - an optional function that determines whether difference analysis should continue down the object graph."

And,
"Pre-filtering Object Properties
The prefilter's signature should be function(path, key) and it should return a truthy value for any path-key combination that should be filtered. If filtered, the difference analysis does no further analysis of on the identified object-property path."

But there is no actual instance of a diff that uses the pre-filter in the readme or examples that I could find. Something showing exactly how to use the following function would be great!

diff.diff(lhs, rhs, function (path, key) {
    //logic
    }
});

The only thing I could find was:

observableDiff(lhs, rhs, function (d) {
    // Apply all changes except those to the 'name' property...
    if (d.path.length !== 1 || d.path.join('.') !== 'name') {
        applyChange(lhs, rhs, d);
    }
});

Which isn't the diff.diff method for one, and doesn't take in two arguments for another.

Awesome package and thanks!

[flitbit]

The readme could use some more detail.

Take a look at the tests, a prefilter tests whether the item at the path and key should be filtered. Any truthy result will cause diff to filter the item.

There are several examples in the tests.

The observableDiff function is an underlying function, the 3rd param is the observer which is called for each difference detected. If you want to call observableDiff, the 4th parameter is the prefilter.

[tnrich]

Awesome, thanks for the feedback. I took a look at the test and it cleared
up using a prefilter with a key. I'll investigate using a prefilter with a
path too since that's the actual operation I want to do.

Cheers,
Thomas

On Mon, Jan 12, 2015, 7:49 PM Phillip Clark notifications@github.com
wrote:

The readme could use some more detail.

Take a look at the tests
https://github.com/flitbit/diff/blob/1bd7cfc7e94a6339568c14046e9eeb205d2a7b7c/test/tests.js#L180-183,
a prefilter tests whether the item at the path and key should be
filtered. Any truthy result will cause diff to filter the item.

There are several examples in the tests.

The observableDiff function is an underlying function, the 3rd param is
the observer which is called for each difference detected. If you want
to call observableDiff, the 4th parameter is the prefilter

diff/index.js

Line 82 in 1bd7cfc

function deepDiff(lhs, rhs, changes, prefilter, path, key, stack) {

.

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