alternate $watch for multiple values

[valtron]

I propose adding another syntax for $watch:

$scope.$watch(['prop', 'foo.bar'], fn);

which would mean the same thing as:

$scope.$watch('prop', fn);
$scope.$watch('foo.bar', fn);

Currently, it's possible to do the same thing using $watchCollection, however:

• $watchCollection supports arbitrary collections; multi-$watch can be optimized better because it's always watching an array, whose size is fixed
• writing the array inside of a string ('[prop, foo.bar]') looks kludgy

But I think the reason for having multi-$watch is mainly semantics (i.e. better communication of intent):

• $watch(['a', 'b'], fn): fn depends on multiple things: a and b
• $watchCollection('collection', fn): fn depends on the contents of one thing: collection

[rodyhaddad]

#6598 will add $scope.$watchSet([exp1, exp2], fn). That's exactly what you're looking for! :-)

Though the naming might change (feel free to give your suggestions in the PR), the PR should land in the coming 1.3.0-beta releases