wp-calypso/client/lib/compare-props/README.md

Comparing object properties

This module exports a helper that creates customized comparator functions to compare objects. The comparator can be configured to compare only selected properties and ignore all other ones, and compare some properties shallowly and other ones deeply.

If no options are specified, the comparator will compare all properties shallowly:

const comparator = compareProps();

// returns true: the property values are strictly equal
comparator( { a: 1 }, { a: 1 } );

// returns false: the property values are not strictly equal
comparator( { a: [] }, { a: [] } );

ignore option

Specify an ignore list of properties that should be ignored by the comparator:

const comparator = compareProps( { ignore: [ 'irrelevant' ] } );

// returns true: the `a` properties are strictly equal and other are irrelevant
comparator(
    {
        a: 1,
        irrelevant: 'whatever1',
    },
    {
        a: 1,
        irrelevant: 'whatever2',
    }
);

deep option

To compare selected properties deeply, specify a deep option:

const comparator = compareProps( { deep: [ 'query' ] } );

// returns true: the `page` properties are are strictly equal and
// the `query` objects are deeply equal, although not identical
comparator(
    {
        query: { text: 'plugin' },
        page: 2,
    },
    {
        query: { text: 'plugin' },
        page: 2,
    }
);

shallow option

If you want to compare only some selected properties shallowly, it's more convenient to enumerate them in a shallow option instead of a long ignore list. This option also comes handy if the compared objects can have arbitrary extra properties that are not relevant for the comparison.

const comparator = compareProps( { shallow: [ 'id' ] } );

// returns true: the `id` properties are strictly equal and all others are ignored
comparator(
    {
        id: 1,
        is_jetpack: true,
    },
    {
        id: 1,
        is_domain_only: true,
    }
);