I'm diving into the world of AngularJS and I'd love for someone to help me understand the distinctions among the AngularJS operators: &, @, and = when working with isolated scopes. Can you provide a detailed example?
I'm diving into the world of AngularJS and I'd love for someone to help me understand the distinctions among the AngularJS operators: &, @, and = when working with isolated scopes. Can you provide a detailed example?
@ is a directive attribute that enables passing a value to the directive's isolate scope from the parent scope. This can be a simple string like myattr="hello" or an AngularJS interpolated string with expressions like myattr="my_{{helloText}}". It facilitates one-way communication between the parent and child scopes. For more detailed explanations, check out John Lindquist's series of short screencasts on this topic. You can find the screencast on @ [here](https://egghead.io/lessons/angularjs-isolate-scope-attribute-binding).
& allows values from the directive's isolate scope to flow into the parent scope for evaluation within the defined expression in the attribute. Remember that the directive attribute itself is implicitly an expression and does not require double curly brace syntax. Understanding this concept may be more challenging through text alone, so don't miss the screencast explanation available [here](https://egghead.io/lessons/angularjs-isolate-scope-expression-binding).
= establishes a two-way binding expression between the directive's isolate scope and the parent scope, ensuring changes propagate bidirectionally. It essentially combines functionalities of both @ and &. Watch the dedicated screencast on = [here](https://egghead.io/lessons/angularjs-isolate-scope-two-way-binding) for further insights.
Lastly, there is a comprehensive screencast demonstrating the utilization of all three methods together in a single view: [link here](https://egghead.io/lessons/angularjs-isolate-scope-review).
Explaining the principles through JavaScript prototype inheritance perspective to aid in comprehension.
Three choices exist for defining directive scope:
scope: false: Default in Angular. Directive's scope aligns with its parentScope.scope: true: Scope created for this directive, prototypically inherits from parentScope.scope: {...}: Explained as isolated scope below.Defining scope: {...} creates an isolatedScope. It does not inherit properties from parentScope, however
isolatedScope.$parent === parentScopeapp.directive("myDirective", function() {
return {
scope: {
... // no inheritance from parent.
},
}
})
isolatedScope lacks direct access to parentScope. Communication is done via @, =, and &. Focus on using symbols @, =, and & with isolatedScope scenarios.
Mainly used for common components shared among pages like Modals. Isolated scope prevents global scope pollution and facilitates sharing among pages.
A basic directive example: http://jsfiddle.net/7t984sf9/5/. Illustrated image here:
@: one-way binding@ passes property value from parentScope to isolatedScope. Known as one-way binding; modifying parentScope properties isn't allowed. Understandable through JavaScript inheritance analogies:
For primitive types like interpolatedProp: you can modify interpolatedProp only; alteration of parentProp1 won't reflect. Changing parentProp1's value overwrites interpolatedProp (during angular $digest).
With object properties like parentObj: reference passing results in error upon value modification - "
TypeError: Cannot assign to read-only property 'x' of {"x":1,"y":2}=: two-way binding= enables two-way binding, allowing modifications in childScope to update
parentScope</code, and vice versa. Applies to both primitives and objects. Transformation example by changing binding type of <code>parentObj=.
&: function binding& permits calling parentScope function from directive and inputting a value. Check out JSFiddle: & in directive scope.
Create clickable template within the directive:
<div ng-click="vm.onCheck({valueFromDirective: vm.value + ' is from the directive'})">
Implement directive like:
<div my-checkbox value="vm.myValue" on-check="vm.myFunction(valueFromDirective)"></div>
valueFromDirective variable transfers from directive to parent controller via {valueFromDirective: ....
Reference: Understanding Scopes
While this isn't my own creation, a great example of the concept can be found at http://jsfiddle.net/maxisam/QrCXh/. Here's the crucial part:
scope:{
/* It's worth noting that in most cases, attributes and bindings share the same name. However, for the purpose of distinguishing between parent and isolated scopes, I've made them distinct here. */
isolatedAttributeFoo:'@attributeFoo',
isolatedBindingFoo:'=bindingFoo',
isolatedExpressionFoo:'&'
}
@: single direction binding
=: dual direction binding
&: method binding
Understanding AngularJS Isolated Scopes: @ vs = vs &
If you're looking for short examples and explanations, check out the link below:
@ - One-way Binding
When used in a directive:
scope : { nameValue : "@name" }
In the view:
<my-widget name="{{nameFromParentScope}}"></my-widget>
= - Two-way Binding
When used in a directive:
scope : { nameValue : "=name" },
link : function(scope) {
scope.name = "Changing the value here will get reflected in parent scope value";
}
In the view:
<my-widget name="{{nameFromParentScope}}"></my-widget>
& - Function Call
When used in a directive:
scope : { nameChange : "&" }
link : function(scope) {
scope.nameChange({newName:"NameFromIsolatedScope"});
}
In the view:
<my-widget nameChange="onNameChange(newName)"></my-widget>
After a significant amount of time, I finally grasped the concept behind this. The crucial realization for me was that "@" is used for items you want evaluated in situ and passed through as a constant into the directive, while "=" actually passes the object itself.
If you're looking for more information on this topic, there's a helpful blog post available at:
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