Directive template unique IDs for elements in AngularJS - angularjs

Question

I have a directive that can be used multiple times on a page. In the template of this directive, I need to use IDs for an input-Element so I can "bind" a Label to it like so:
<input type="checkbox" id="item1" /><label for="item1">open</label>
Now the problem is, as soon as my directive is included multiple times, the ID "item1" is not unique anymore and the label doesn't work correctly (it should check/uncheck the checkbox when clicked).
How is this problem fixed? Is there a way to assign a "namespace" or "prefix" for the template (like asp.net does with the ctl00...-Prefix)? Or do I have to include an angular-Expression in each id-Attribute which consists of the directive-ID from the Scope + a static ID. Something like:
<input type="checkbox" id="{{directiveID}} + 'item1'" /><label for="{{directiveID}} + 'item1'">open</label>
Edit:
My Directive
module.directive('myDirective', function () {
return {
restrict: 'E',
scope: true,
templateUrl: 'partials/_myDirective.html',
controller: ['$scope', '$element', '$attrs', function ($scope, $element, $attrs) {
...
} //controller
};
}]);
My HTML
<div class="myDirective">
<input type="checkbox" id="item1" /><label for="item1">open</label>
</div>

Answer 1

HTML
<div class="myDirective">
<input type="checkbox" id="myItem_{{$id}}" />
<label for="myItem_{{$id}}">open myItem_{{$id}}</label>
</div>

Answer 2

UPDATE
Angular 1.3 introduced a native lazy one-time binding. from the angular expression documentation:
One-time binding
An expression that starts with :: is considered a
one-time expression. One-time expressions will stop recalculating once
they are stable, which happens after the first digest if the
expression result is a non-undefined value (see value stabilization
algorithm below).
Native Solution:
.directive('myDirective', function() {
var uniqueId = 1;
return {
restrict: 'E',
scope: true,
template: '<input type="checkbox" id="{{::uniqueId}}"/>' +
'<label for="{{::uniqueId}}">open</label>',
link: function(scope, elem, attrs) {
scope.uniqueId = 'item' + uniqueId++;
}
}
})
Only bind once:
If you only need to bind a value once you should not use bindings ({{}} / ng-bind)
bindings are expensive because they use $watch. In your example, upon every $digest, angular dirty checks your IDs for changes but you only set them once.
Check this module: https://github.com/Pasvaz/bindonce
Solution:
.directive('myDirective', function() {
var uniqueId = 1;
return {
restrict: 'E',
scope: true,
template: '<input type="checkbox"/><label>open</label>',
link: function(scope, elem, attrs) {
var item = 'item' + uniqueId++;
elem.find('input').attr('id' , item);
elem.find('label').attr('for', item);
}
}
})

Answer 3

We add a BlockId parameter to the scope, because we use the id in our Selenium tests for example. There is still a chance of them not being unique, but we prefer to have complete control over them. Another advantage is that we can give the item a more descriptive id.
Directive JS
module.directive('myDirective', function () {
return {
restrict: 'E',
scope: {
blockId: '#'
},
templateUrl: 'partials/_myDirective.html',
controller: ['$scope', '$element', '$attrs', function ($scope, $element, $attrs) {
...
} //controller
};
}]);
Directive HTML
<div class="myDirective">
<input type="checkbox" id="{{::blockId}}_item1" /><label for="{{::blockId}}_item1">open</label>
</div>
Usage
<my-directive block-id="descriptiveName"></my-directive>

Answer 4

Apart from Ilan and BuriB's solutions (which are more generic, which is good) I found a solution to my specific problem because I needed IDs for the "for" Attribute of the label. Instead the following code can be used:
<label><input type="checkbox"/>open</label>
The following Stackoverflow-Post has helped:
https://stackoverflow.com/a/14729165/1288552