Gracias Daniel,
Angular is good because it don't force you to follow any convention so you
have the liberty of doing things like you want. That could be a double-edge
sword. That liberty is good but sometimes it is hard to pickup some
conventions that are good to follow.
Your explanation was really awesome. It is sometimes hard to understand
some conventions by logic so this answer is really appreciated.
I am writing a bunch of recipes to help beginners and I wasn't able to see
the reasons behind those decision.
About the =?. I was thinking about a recipe for that too but I was thinking
about a use case and as you say, it is pretty rare so I will leave that
out, I don't think in any use case that could help a beginner.
Thanks again.
On Monday, December 23, 2013 10:25:47 AM UTC+1, Daniel Tabuenca wrote:
>
> The difference between declaring stuff in the scope: {} vs just reading
> the attributes inside the link function has to do primarily with whether we
> want to keep track of the values as they change. Things declared in the
> isolate scope will automatically get watches created to keep them in sync
> with the outside scope or expression.
>
> In general, if you only need a value once when setting up the structure of
> your directive, but don’t need to keep it updated live, then it is better
> to keep it outside of the scope declaration, and simply read it from the
> attributes (usually by either using $scope.$eval() or $interpolate.
>
> This brings us to your second question. The choice between $interpolate()or
> $scope.$eval() really just comes down to how you expect people to use
> your directive. For attributes that you expect people to mostly put literal
> text values directly in the template (rather than using a variable in the
> scope), you would likely chose to $interpolate(). For example, say I have
> a fancy label directive that takes the text to place on the label:
>
> <my-label text="This is my label" />
>
> This seems like a good candidate for $interpolate(). If you didn’t use
> $interpolate I would force people to have to quote the text:
>
> <my-label text=" 'This is my label' "/>
>
> On the other hand, say I have a hello directive that outputs the name of
> the currently logged in person. This would more likely be a candidate for
> $scope.$eval() since the common usage would be to use something already
> declared in the scope:
>
> <say-hello to="currentUser.name"/>
>
> If I used interpolation I would have to add some extra braces:
>
> <say-hello to="{{currentUser.name}}"/>
>
> So the basic rule of thumb to me is this:
>
> If the typical case for the attribute is to read a value stored in the
> scope, then use $eval instead of $interpolate.
>
> If the typical case is for the user to have a literal string in the html
> template, use $interpolate instead of $eval.
>
> If the attribute expects a non-string primitive value (e.g. an int or a
> boolean) then you should probably use $eval since $interpolate will always
> return a string.
>
> As far as a use case for “=?”. This is not very common. Remember, plain
> “=” creates a two-way binding between a variable OUTSIDE the isolate scope
> and one INSIDE the isolate scope. This usually means you want to read and
> write to the variable in the OUTSIDE scope by modifying the variable in the
> ISOLATE scope.
>
> If the argument you pass in does not exist, reading will work fine (it
> will just read a blank or undefined value). However, if you tried to write
> to the scope variable, you would get an “Expression ‘undefined’ used with
> directive is non-assignable!” exception.
>
> Using “=?” makes the directive able to work in the case where the variable
> does not exist in the OUTER scope by just reading/writing to a variable in
> the ISOLATE scope (but not synchronizing with the outer scope at all).
>
> For example you need to use “=?” to make the following directive work if
> you didin’t pass it a name:
>
> app.directive('hello', function(){
> return {
> scope:{
> name: '=?'
> },
> template: '<div>'+
> '<input ng-model="name"/>'+
> '<p>Hello {{name}}</p>'+
> '</div>'
> };
> })
>
> A situation where you need this is rare though. For most optional
> parameters you should not need to use it.
>
--
You received this message because you are subscribed to the Google Groups
"AngularJS" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/angular.
For more options, visit https://groups.google.com/groups/opt_out.
