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JS: AngularJS Directive Attribute Binding Explanation

AngularJS Directive Attribute Binding Explanation

When using directives, you often need to pass parameters to the directive. This can be done in several ways. The first 3 can be used whether scope is true or false. This is still a WIP, so validate for yourself.

  1. Raw Attribute Strings

    <div my-directive="some string" another-param="another string"></div>
    
    var directiveFunction = function(){
    	return {
    		link: function(scope, element, attributes){
    
    			console.log(attributes.myDirective);
    			console.log(attributes.anotherParam);
    
    		}
    	};
    }
  2. Observing Interpolated Strings (Also Watches for Changes)

    <div my-directive="{{some string}}" another-param="another string"></div>
    
    var directiveFunction = function(){
    	return {
    		link: function(scope, element, attributes){
    		
    			console.log(attributes.myDirective); //literal string "{{some string}}", no interpolation
    			console.log(attributes.anotherParam); //literally "another string"
    
    			attributes.$observe('myDirective', function(value){
    				console.log(value);
    			});
    
    			attributes.$observe('anotherParam', function(value){
    				console.log(value);
    			});
    
    		}
    	};
    }
  3. Observing Expression Strings (Also watches for changes)

    <div my-directive="modelObject" another-param="modelObject.obj"></div>
    
    var directiveFunction = function(){
    	return {
    		link: function(scope, element, attributes){
    		
    			console.log(attributes.anotherParam); //literally "modelObject.obj"
    		
    			//modelObject is a scope property of the parent/current scope
    			scope.$watch(attributes.myDirective, function(value){
    				console.log(value);
    			});
    			
    			//modelObject.obj is also a scope property of the parent/current scope
    			scope.$watch(attributes.anotherParam, function (value){
    				console.log(value);
    			});
    			
    			//if you tried to use $observe, you would get the literal expression "modelObject" and "modelObject.obj", because there's nothing to interpolate
    
    		}
    	};
    }
  4. Evaluating Object Expressions

    <div my-directive="{ param: 34, param2: 'cool' }" another-param="another string"></div>
    
    var directiveFunction = function(){
    	return {
    		link: function(scope, element, attributes){
    
    			//this is designed for directive configuration if there's a alot of configuration parameters
    			//one can combine this with interpolation, if the configuration is a JSON string
    			var obj = scope.$eval(attributes.myDirective);
    			//can also fallback as a string
    			var string = scope.$eval(attributes.anotherParam);
    
    			console.log(obj);
    			console.log(string);
    
    		}
    	};
    }
  5. Isolate Scope One Way String Binding (Parent changes affect child, child changes does not affect parent)

    <div my-directive="{{some.string}}" another-param="{{another.string}}" string-param="somestring"></div>
    
    var directiveFunction = function(){
    	return {
    		scope: {
    			myDirective: '@',
    			anotherParam: '@',
    			stringParam: '@'
    		},
    		link: function(scope, element, attributes){
    
    			//the '@' binding automatically interpolates the "{{}}" if they exist in the attributes
    			console.log(scope.myDirective); //interpolated string
    			console.log(scope.anotherParam); //interpolated string
    			console.log(scope.stringParam); //literal string
    			
    			//IMPORTANT: if scope.some.string was not defined on the parent scope, then '@' interpolates it into an EMPTY string, it is still a STRING type
    			//if the DOM attribute was not defined, scope.property would returned undefined
    
    			//if the strings are not yet processed when this directive runs
    			//this means they are interpolated, but perhaps the true value has not arrived, such as content from AJAX
    			//see: http://stackoverflow.com/a/14907826/582917
    			attributes.$observe('myDirective', function(value){
    				if(value){
    					console.log(value);
    				}
    			});
    			attributes.$observe('anotherParam', function(value){
    				if(value){
    					console.log(value);
    				}
    			});
    
    			//the $watch method also works because the '@' binding already does the interpolation
    			//see: http://stackoverflow.com/a/12976630/582917 & http://stackoverflow.com/a/17224886/582917
    			//this only works because it's in an isolate scope, therefore myDirective is part of the scope
    			scope.$watch('myDirective', function(value){
    				if(value){
    					console.log(value);
    				}
    			});
    			
    			//the difference between $observe and $watch in this context, is that $observe reruns the interpolation (from the literal attribute value) and watches the value change, whereas the $watch relies on the '@' interpolation and parent binding and simply watches the value change in this current isolated scope
    			//this means if want to react to the value change coming from this directive, you'll need to use $watch, otherwise if you only want to react to parent changes, you may use $observe
    			
    			//multivalue value watching, only possible with $watch
    			//make sure to assign an object outside of the scope
    			//if you decide to return an object "return { }", a new object reference would be created
    			//inside the watch, and thus trigger another watch, resulting in digest errors
    			//MAKE SURE TO DO DEEP WATCH!
    			var multiValues = {};
    			scope.$watch(function(){
    				multiValues.myDirective = scope.myDirective;
    				multiValues.anotherParam = scope.anotherParam;
    				return multiValues;
    			}, function(value){
    				if(value){
    					console.log(value);
    				}
    			}, true);
    
    		}
    	};
    }
  6. Isolate Scope Two Way Object Binding (Parent changes affect child and child changes affect parent)

    <div my-directive="modelObject" another-param="{ thisWill: 'result in digest errors' }"></div>
    
    var directiveFunction = function(){
    	return {
    		scope: {
    			myDirective: '=', //use =? for optionality
    			anotherParam: '='
    		},
    		link: function(scope, element, attributes){
    
    			//modelObject needs to be defined on the parent scope or you can use "=?" for optionality
    			console.log(scope.myDirective); //this will be the parent/current scope's value, it's not the literal string
    			//this will result in digest errors: http://stackoverflow.com/q/13594732/582917
    			//so don't use object expressions with '='
    			console.log(scope.anotherParam);
    			
    			//IMPORTANT: if scope.modelObject was not defined on the parent scope, then '=' interpolates it into an UNDEFINED type, this works for child objects as well like scope.modelObject.childObject
    			//if the DOM attribute was not defined, scope.property would returned undefined
    
    			//the $watch method works when the model values have not yet been processed by the time this directive runs
    			scope.$watch('myDirective', function(value){
    				if(value){
    					console.log(value);
    				}
    			});
    			
    			//$observe is useless here, as there is no interpolation whatsoever, the $watch will react to changes from both parent scope and current scope, furthermore any change to the value here, changes the parent value as well
    			
    			//=? is required if you want to assign values to the current isolated scope property, but the DOM attribute or parent scope property was never defined, checking if it exists or logging its current value won't result in an error
    
    		}
    	};
    }
  7. Isolate Scope Object & Object Literal Expression Binding

    <div my-directive="{ param: 34, param2: 'cool' }" another-param="parentScopeObject"></div>
    
    var directiveFunction = function(){
    	return {
    		scope: {
    			myDirective: '&',
    			anotherParam: '&'
    		},
    		link: function(scope, element, attributes){
    
    			//this will return the actual object from the object expression!
    			console.log(scope.myDirective());
    			//this will return the actual object from the parent scope, if it exists of course!
    			//and no "parentScopeObject" is not a function, it's an object
    			console.log(scope.anotherParam());
    
    		}
    	};
    }
  8. Isolate Scope Function Expression Binding

    <div my-directive="parentScopeFunction(funcParam, secondParam)"></div>
    
    var directiveFunction = function(){
    	return {
    		template: '<button ng-click="myDirective({funcParam: 'blah blah', secondParam: 'blah blah'})">It can be executed from inside the DOM too!</button>',
    		scope: {
    			myDirective: '&'
    		},
    		link: function(scope, element, attributes){
    		
    			//IMPORTANT: if scope.parentScopeFunction was not defined on the parent scope, then '&' interpolates it into a NOOP function, it is still a FUNCTION type
    			//if the DOM attribute was not defined, scope.property would also still return a noop function
    
    			//if it's defined as something other than a function, an error occurs!
    			
    			//parameters passed into the bound function expression must be in the form of an object map
    			scope.myDirective(
    				{
    					funcParam: 'This is the value that is going to be passed in as the funcParam',
    					secondParam: 'This is another param!'
    				}
    			);
    
    		}
    	};
    }
  9. Non-Isolate Scope Function Expression Binding

    <div my-directive="parentScopeFunction(funcParam)" another-func="parentScopeFunction2()"></div>
    
    var directiveFunction = function($parse){
    	return {
    		link: function(scope, element, attributes){
    
    			//see this: 
    			//http://stackoverflow.com/questions/17583004/call-an-angularjs-controller-function-from-a-directive-without-isolated-scope
    			//http://stackoverflow.com/questions/14858682/angularjs-directive-with-isolate-scope-do-i-really-have-to-call-parent-everyw
    			
    			//apply and eval
    			scope.$apply(function() { 
    				scope.$eval(attributes.anotherFunc); 
    			});
    
    			//apply only
    			scope.$apply(attributes.anotherFunc);
    			
    			//$parse method, this allows parameters to be passed
    			var invoker = $parse(attributes.myDirective);
    			invoker(scope, {funcParam: 'example value'});
    
    		}
    	};
    }
@twig2let

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@twig2let twig2let commented Jun 20, 2014

Great reference material, thanks!

@stefanwalther

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@stefanwalther stefanwalther commented Jun 27, 2014

Great collection! Thanks!

@mjdenham

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@mjdenham mjdenham commented Jul 9, 2014

Very helpful, especially 'parameters passed into the bound function expression must be in the form of an object map'.

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@AdityaJitu AdityaJitu commented Oct 4, 2014

Very helpful collection . Thank you !

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@JoachimR JoachimR commented Oct 13, 2014

very clear and easy to read and understand. thank you very much

@Voxelot

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@Voxelot Voxelot commented Oct 16, 2014

Extremely useful, thanks!

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@manojjsm manojjsm commented Oct 29, 2014

Very helpful, Thank You

@jamesbrobb

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@jamesbrobb jamesbrobb commented Nov 6, 2014

Thanks for this.

Anyone know why i always get an error when attempting to call a function expression (No.9) with scope.$apply?

Error: [$rootScope:inprog] $digest already in progress

I've seen it used in loads of examples (for directives) and it's also done that way in the angular source. But i always get an error?

@parsenz

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@parsenz parsenz commented Nov 6, 2014

Incredibly helpful, thanks

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@helmi03 helmi03 commented Nov 11, 2014

thanks, 5 stars

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@unr unr commented Nov 14, 2014

👍 You da bes.

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@karolisg karolisg commented Nov 23, 2014

Very helpful 👍

@Wlada

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@Wlada Wlada commented Feb 18, 2015

Thanks. This helps a lot!

@gopisf

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@gopisf gopisf commented Feb 23, 2015

Good examples for directive. Thank you.

@ghost

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@ghost ghost commented Feb 23, 2015

Best Examples for Directives

@kespeart

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@kespeart kespeart commented Mar 6, 2015

Nice!!!!

@OliPelz

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@OliPelz OliPelz commented Mar 17, 2015

This is so helpful! Thanks a lot!

@dixon629

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@dixon629 dixon629 commented Mar 19, 2015

So helpful,thank u!

@imarkahann

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@imarkahann imarkahann commented Mar 30, 2015

Thanks !

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@sarunast sarunast commented Apr 15, 2015

The 3rd example doesn't work for me 😢

@joshbuchea

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@joshbuchea joshbuchea commented Apr 27, 2015

Very useful. Thanks!

@AsuScholar

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@AsuScholar AsuScholar commented May 15, 2015

This saved me soooo much time! Thanks for the great and detailed explanation!

@antivitla

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@antivitla antivitla commented May 16, 2015

Thought i would never find this - big thanks to such work of collecting really tricky and tiny nuances of using bindings!

@martinmcwhorter

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@martinmcwhorter martinmcwhorter commented May 20, 2015

This should be part of the angular 1.x documentation.

@andresmgsl

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@andresmgsl andresmgsl commented May 30, 2015

You really help me. Thanks

@DvirH

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@DvirH DvirH commented Aug 26, 2015

Great very comprehensive!

@SimoneMSR

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@SimoneMSR SimoneMSR commented Sep 18, 2015

This guide is very intriguing and complete. BTW, Example 3 does not watches for changes of existing modelObject, for me. Can you confirm, or instead better explain?

@eventures-io

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@eventures-io eventures-io commented Oct 2, 2015

Very clear. Thanks!

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@Jakobovski Jakobovski commented Oct 26, 2015

+10

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@watcharaphong watcharaphong commented Nov 12, 2015

Very helpful Thank you

6 -> Isolate Scope Two Way Object Binding (Parent chnages -> change affect child and child changes affect parent)

@mujuni88

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@mujuni88 mujuni88 commented Nov 17, 2015

Very helpful. Thank you a lot.

@peterdouglas

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@peterdouglas peterdouglas commented Nov 25, 2015

Great guide. Thank you!

@laradevitt

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@laradevitt laradevitt commented Nov 25, 2015

This was a great help. Thanks!

@Amitesh

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@Amitesh Amitesh commented Dec 2, 2015

Awesome!!

@ulesta

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@ulesta ulesta commented Dec 8, 2015

Awesome! Just what I needed! These should go up as examples in the actual docs!

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@secmax secmax commented Dec 17, 2015

helpful, thanks

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@rootux rootux commented Dec 31, 2015

Another interesting way is to use rootScope (Yes it's a bad habit).
you can define a function / variable on the rootscope and then access it.
If you are using a directive which has an isolated scope make sure you use $root like so: $scope.$root.myFunc()

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@qfish qfish commented Jan 8, 2016

This was a great help. Thanks!

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@gabrielfeitosa gabrielfeitosa commented Jan 27, 2016

Great material! Thanks for sharing

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@g3xx g3xx commented Feb 2, 2016

Thanks Om ! 👍

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@aureustaurus aureustaurus commented Feb 4, 2016

Thanks! very helpful!

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@bastianwegge bastianwegge commented Feb 8, 2016

great stuff !

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@taotau taotau commented Feb 24, 2016

Angular binding in a nutshell. Thanks for the lightbulb moment!

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@chacaldev chacaldev commented Feb 26, 2016

Thanks!!! Really helpful!

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@paladinwitzy paladinwitzy commented Mar 24, 2016

Very helpful, thanks for sharing.

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@anilsingh581 anilsingh581 commented Mar 26, 2016

It might help you for Attribute Binding in Angular
http://www.code-sample.com/2016/03/auto-capitalize-input-char-using.html

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@AndreyUtka AndreyUtka commented Apr 7, 2016

What about one way expression bindings? ::item

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@laranicolas laranicolas commented Apr 7, 2016

Thanks for sharing!

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@jamesjryan jamesjryan commented Apr 18, 2016

Sending more thanks your way.

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@Chima1707 Chima1707 commented Apr 23, 2016

Very helpful

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Owner Author

@CMCDragonkai CMCDragonkai commented Jun 2, 2016

Thanks for all the feedback. This gist was written 2 years ago, and things may have changed in Angular in the mean time. Though a lot probably still applies. If any of you improve on it, feel free to fork it and put it up, or suggest a diff to apply to the gist above, and I'll update it, but I'm not able to verify whether any new changes works.

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@CMCDragonkai CMCDragonkai commented Jun 14, 2016

By the way, I've worked on a project callee SnapSearch (https://snapsearch.io/) that allowd sites built in AngularJS and any Javascript framework to be indexed by search engines and social network robots. Might be useful to people frequenting this gist.

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@saucey saucey commented Aug 6, 2016

good stuff

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@gilderlan gilderlan commented Aug 29, 2016

\o/

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@AndrewIsh AndrewIsh commented Sep 20, 2016

Excellent resource, thanks. Any chance you could break the comments? Having to scroll horizontally to read them is a PITA :)

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@abhishekbhalani abhishekbhalani commented Oct 22, 2016

Good stuff.. thank you 💯

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@mdeggies mdeggies commented Nov 6, 2016

Saved my butt. Thank you!

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@NithinBiliya NithinBiliya commented Dec 22, 2016

great material!

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@bb-swapnil bb-swapnil commented Mar 21, 2017

could not stop myself to say ' Its AWESOME" .... !!!!

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@sserbest sserbest commented Mar 28, 2017

Very helpful, thanks.

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@TSkills TSkills commented Apr 12, 2017

Nice nice nice !!

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@wuxicn wuxicn commented Apr 20, 2017

Awesome! Thank you!

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@BurakAkyildiz BurakAkyildiz commented Jun 14, 2017

Non isolated binding was helpfull thnx..

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@avrim-tr avrim-tr commented Aug 4, 2017

HI,

In Example 2,
console.log(attributes.myDirective) WILL BE ITERPULATED

@TatyanaDubrova

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@TatyanaDubrova TatyanaDubrova commented Nov 27, 2017

Cool explanation, thank you so much

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@fantasiiio fantasiiio commented Mar 1, 2018

Thank you very much !

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@milad1367 milad1367 commented May 22, 2018

Thanks, man!

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@RobertRajcool RobertRajcool commented Jul 23, 2018

Great article

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@james-jhang james-jhang commented Oct 7, 2018

Thank you

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@NewEXE NewEXE commented Nov 11, 2020

Thanks from 2020 :-)

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