how to set an interpolated value in angular directive? - angularjs

Question

How do I set the interpolated value in a directive? I can read the correct value from the following code, but I have not been able to set it.
js:
app.directive('ngMyDirective', function () {
return function(scope, element, attrs) {
console.log(scope.$eval(attrs.ngMyDirective));
//set the interpolated attrs.ngMyDirective value somehow!!!
}
});
html:
<div ng-my-directive="myscopevalue"></div>
where myscopevalue is a value on my controller's scope.

Answer 1

Whenever a directive does not use an isolate scope and you specify a scope property using an attribute, and you want to change that property's value, I suggest using $parse. (I think the syntax is nicer than $eval's.)
app.directive('ngMyDirective', function ($parse) {
return function(scope, element, attrs) {
var model = $parse(attrs.ngMyDirective);
console.log(model(scope));
model.assign(scope,'Anton');
console.log(model(scope));
}
});
fiddle
$parse works whether or not the attribute contains a dot.

Answer 2

If you want to set a value on the scope but don't know the name of the property (ahead of time), you can use object[property] syntax:
scope[attrs.myNgDirective] = 'newValue';
If the string in the attribute contains a dot (e.g. myObject.myProperty), this won't work; you can use $eval to do an assignment:
// like calling "myscopevalue = 'newValue'"
scope.$eval(attrs.myNgDirective + " = 'newValue'");
[Update: You should really use $parse instead of $eval. See Mark's answer.]
If you're using an isolate scope, you can use the = annotation:
app.directive('ngMyDirective', function () {
return {
scope: {
theValue: '=ngMyDirective'
},
link: function(scope, element, attrs) {
// will automatically change parent scope value
// associated by the variable name given to `attrs.ngMyDirective`
scope.theValue = 'newValue';
}
}
});
You can see an example of this in this Angular/jQuery color picker JSFiddle example, where assigning to scope.color inside the directive automatically updates the variable passed into the directive on the controller's scope.