I'm fairly new with AngularJS so please excuse my ignorance and improper terminology.
I have a Controller called activitiesController that returns an array of activity objects. Each activity object has some properties which I can display in the view using ng-repeat="activity in activities".
One of the properties is a big string that I need to hack apart and essentially add to new properties of the activity object (I know this is horrible but it's from a legacy system).
Do I run a function in ng-repeat like ng-repeat="activity in getNewProperties(activities)" where I would loop through each activity and return the array back to ng-repeat.
OR
Do I just make a function in the scope that will return each property that I'm looking for.
Ideally in the view I would just use activity.newDetails.NewValue which makes me beielve i need to run my function on all of the activity objects before they are passed to ng-repeat in the view.
Sorry I know this isn't very details I can try to add more shortly.
Do I run a function in ng-repeat like ng-repeat="activity in getNewProperties(activities)" where I would loop through each activity and return the array back to ng-repeat.
Let's say you did this and the function looks something like this:
$scope.getNewProperties = function(activities) {
var modifiedActivities = [];
for (var i = 0; i < activities.length; i++) {
var modifiedActivity = activities[i];
modifiedActivity.foo = "bar";
modifiedActivities.push(modifiedActivity);
}
return modifiedActivities;
};
This function will run in every $digest cycle. Besides from being resource consuming, it also means that if you make changes to modified properties (in this case foo), the next time this function runs, the property will be overwritten by this function.
What you want to do is modify $scope.activities as soon as you get the data. This way it will only occur once unless you refresh the data. e.g.
$http.get("http://somewebsite/api").then(function(response) {
$scope.activities = response.data;
for (var i = 0; i < $scope.activities.length; i++) {
// modify properties
}
});
Here's my code:
<h1 ng-repeat="item in func()">something</h1>
$scope.func = function(){
return [{"property" : "value1"},{"property": "value2"}];
}
In Angular.js v. 1.1.1 there's no mistake. In Angular.JS v 1.2.1 I get an infDig mistake.
Fiddle of v.1.1.1
Fiddle of v.1.2.1
Could you explain this situation? Thanks a lot.
As of AngularJS 1.2: The "track by" expression was added to ng-repeat and more appropriately addresses this issue as demonstrated
in the following code.
<h1 ng-repeat="item in func() track by $index">something</h1>
$scope.func = function(){
return [{"property" : "value1"},{"property": "value2"}];
}
The following article helps understand the expression in more detail and why it is so useful, particularly when dealing with $$haskey Using Track-By With ngRepeat In AngularJS 1.2 by Ben Nadal.
The problem is that you're creating a new array each time, so it's something new that angular needs to track. As far as I can tell, ng-repeat runs, then immediately checks its collection again to see if anything changed in that cycle. Because the function returns a new array, that is perceived as a change.
Check this out: http://jsfiddle.net/kL5YZ/.
If you look in the console.log and click the button, you will see that the $$hashKey property of the objects is being changed each time ng-repeat runs.
The change occurs starting at version 1.1.4, but the changelog doesn't give any clues as to why the behavior is different. The new behavior does make more sense to me.
Here's a great post I found explaining the current behavior in depth: How to Loop through items returned by a function with ng-repeat?
If you make sure to return the same object/array each time, you won't have the error. You could have the function cache anything it creates based on the arguments and always return the same array/object when those arguments are passed in. So, myFunc('foo') will always return the same array, not a new one that looks the same. See the notes in my code below. Live demo (click).
<div ng-repeat="foo in foos">
<div ng-repeat="bar in barFunc(foo)">{{bar.text}}</div>
<div ng-repeat="bar in barFunc('test')">{{bar.text}}</div>
</div>
JavaScript:
var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope, myService) {
$scope.foos = [
'a','b','c'
];
//I put this into a service to avoid cluttering the controller
$scope.barFunc = myService.getObj;
});
app.factory('myService', function() {
/*
* anything created will be stored in this cache object,
* based on the arguments passed to `getObj`.
* If you need multiple arguments, you could form them into a string,
* and use that as the cache key
* since there's only one argument here, I'll just use that
*/
var cache = {};
var myService = {
getObj : function(val) {
//if we haven't created an array with this argument before
if (!cache[val]) {
//create one and store it in the cache with that argument as the key
cache[val] = [
{text:val}
];
}
//return the cached array
return cache[val];
}
};
return myService;
});
I receive data from my back end server structured like this:
{
name : "Mc Feast",
owner : "Mc Donalds"
},
{
name : "Royale with cheese",
owner : "Mc Donalds"
},
{
name : "Whopper",
owner : "Burger King"
}
For my view I would like to "invert" the list. I.e. I want to list each owner, and for that owner list all hamburgers. I can achieve this by using the underscorejs function groupBy in a filter which I then use in with the ng-repeat directive:
JS:
app.filter("ownerGrouping", function() {
return function(collection) {
return _.groupBy(collection, function(item) {
return item.owner;
});
}
});
HTML:
<li ng-repeat="(owner, hamburgerList) in hamburgers | ownerGrouping">
{{owner}}:
<ul>
<li ng-repeat="burger in hamburgerList | orderBy : 'name'">{{burger.name}}</li>
</ul>
</li>
This works as expected but I get an enormous error stack trace when the list is rendered with the error message "10 $digest iterations reached". I have a hard time seeing how my code creates an infinite loop which is implied by this message. Does any one know why?
Here is a link to a plunk with the code: http://plnkr.co/edit/8kbVuWhOMlMojp0E5Qbs?p=preview
This happens because _.groupBy returns a collection of new objects every time it runs. Angular's ngRepeat doesn't realize that those objects are equal because ngRepeat tracks them by identity. New object leads to new identity. This makes Angular think that something has changed since the last check, which means that Angular should run another check (aka digest). The next digest ends up getting yet another new set of objects, and so another digest is triggered. The repeats until Angular gives up.
One easy way to get rid of the error is to make sure your filter returns the same collection of objects every time (unless of course it has changed). You can do this very easily with underscore by using _.memoize. Just wrap the filter function in memoize:
app.filter("ownerGrouping", function() {
return _.memoize(function(collection, field) {
return _.groupBy(collection, function(item) {
return item.owner;
});
}, function resolver(collection, field) {
return collection.length + field;
})
});
A resolver function is required if you plan to use different field values for your filters. In the example above, the length of the array is used. A better be to reduce the collection to a unique md5 hash string.
See plunker fork here. Memoize will remember the result of a specific input and return the same object if the input is the same as before. If the values change frequently though then you should check if _.memoize discards old results to avoid a memory leak over time.
Investigating a bit further I see that ngRepeat supports an extended syntax ... track by EXPRESSION, which might be helpful somehow by allowing you to tell Angular to look at the owner of the restaurants instead of the identity of the objects. This would be an alternative to the memoization trick above, though I couldn't manage to test it in the plunker (possibly old version of Angular from before track by was implemented?).
Okay, I think I figured it out. Start by taking a look at the source code for ngRepeat. Notice line 199: This is where we set up watches on the array/object we are repeating over, so that if it or its elements change a digest cycle will be triggered:
$scope.$watchCollection(rhs, function ngRepeatAction(collection){
Now we need to find the definition of $watchCollection, which begins on line 360 of rootScope.js. This function is passed in our array or object expression, which in our case is hamburgers | ownerGrouping. On line 365 that string expression is turned into a function using the $parse service, a function which will be invoked later, and every time this watcher runs:
var objGetter = $parse(obj);
That new function, which will evaluate our filter and get the resulting array, is invoked just a few lines down:
newValue = objGetter(self);
So newValue holds the result of our filtered data, after groupBy has been applied.
Next scroll down to line 408 and take a look at this code:
// copy the items to oldValue and look for changes.
for (var i = 0; i < newLength; i++) {
if (oldValue[i] !== newValue[i]) {
changeDetected++;
oldValue[i] = newValue[i];
}
}
The first time running, oldValue is just an empty array (set up above as "internalArray"), so a change will be detected. However, each of its elements will be set to the corresponding element of newValue, so that we expect the next time it runs everything should match and no change will be detected. So when everything is working normally this code will be run twice. Once for the setup, which detects a change from the initial null state, and then once again, because the detected change forces a new digest cycle to run. In the normal case no changes will be detected during this 2nd run, because at that point (oldValue[i] !== newValue[i]) will be false for all i. This is why you were seeing 2 console.log outputs in your working example.
But in your failing case, your filter code is generating a new array with new elments every time it's run. While this new array's elments have the same value as the old array's elements (it's a perfect copy), they are not the same actual elements. That is, they refer to different objects in memory that simply happen to have the same properties and values. Hence in your case oldValue[i] !== newValue[i] will always be true, for the same reason that, eg, {x: 1} !== {x: 1} is always true. And a change will always be detected.
So the essential problem is that your filter is creating a new copy of the array every time it's run, consisting of new elements that are copies of the original array's elments. So the watcher setup by ngRepeat just gets stuck in what is essentially an infinite recursive loop, always detecting a change and triggering a new digest cycle.
Here's a simpler version of your code that recreates the same problem: http://plnkr.co/edit/KiU4v4V0iXmdOKesgy7t?p=preview
The problem vanishes if the filter stops creating a new array every time it's run.
New to AngularJS 1.2 is a "track-by" option for the ng-repeat directive. You can use it to help Angular recognize that different object instances should really be considered the same object.
ng-repeat="student in students track by student.id"
This will help unconfuse Angular in cases like yours where you're using Underscore to do heavyweight slicing and dicing, producing new objects instead of merely filtering them.
Thanks for the memoize solution, it works fine.
However, _.memoize uses the first passed parameter as the default key for its cache. This could not be handy, especially if the first parameter will always be the same reference. Hopefully, this behavior is configurable via the resolver parameter.
In the example below, the first parameter will always be the same array, and the second one a string representing on which field it should be grouped by:
return _.memoize(function(collection, field) {
return _.groupBy(collection, field);
}, function resolver(collection, field) {
return collection.length + field;
});
Pardon the brevity, but try ng-init="thing = (array | fn:arg)" and use thing in your ng-repeat. Works for me but this is a broad issue.
I am not sure why this error is coming but, logically the filter function gets called for each element for the array.
In your case the filter function that you have created returns a function which should only be called when the array is updated, not for each element of the array. The result returned by the function can then be bounded to html.
I have forked the plunker and have created my own implementation of it here http://plnkr.co/edit/KTlTfFyVUhWVCtX6igsn
It does not use any filter. The basic idea is to call the groupBy at the start and whenever an element is added
$scope.ownerHamburgers=_.groupBy(hamburgers, function(item) {
return item.owner;
});
$scope.addBurger = function() {
hamburgers.push({
name : "Mc Fish",
owner :"Mc Donalds"
});
$scope.ownerHamburgers=_.groupBy(hamburgers, function(item) {
return item.owner;
});
}
For what it's worth, to add one more example and solution, I had a simple filter like this:
.filter('paragraphs', function () {
return function (text) {
return text.split(/\n\n/g);
}
})
with:
<p ng-repeat="p in (description | paragraphs)">{{ p }}</p>
which caused the described infinite recursion in $digest. Was easily fixed with:
<p ng-repeat="(i, p) in (description | paragraphs) track by i">{{ p }}</p>
This is also necessary since ngRepeat paradoxically doesn't like repeaters, i.e. "foo\n\nfoo" would cause an error because of two identical paragraphs. This solution may not be appropriate if the contents of the paragraphs are actually changing and it's important that they keep getting digested, but in my case this isn't an issue.
I have an array of items bound to <li> elements in a <ul> with AngularJS. I want to be able to click "remove item" next to each of them and have the item removed.
This answer on StackOverflow allows us to do exactly that, but because the name of the array which the elements are being deleted from is hardcoded it is not usable across lists.
You can see an example here on JSfiddle set up, if you try clicking "remove" next to a Game, then the student is removed, not the game.
Passing this back from the button gives me access to the Angular $scope at that point, but I don't know how to cleanly remove that item from the parent array.
I could have the button defined with ng-click="remove('games',this)" and have the function look like this:
$scope.remove = function (arrayName, scope) {
scope.$parent[arrayName].splice(scope.$index,1);
}
(Like this JSFiddle) but naming the parent array while I'm inside it seems like a very good way to break functionality when I edit my code in a year.
Any ideas?
I did not get why you were trying to pass this .. You almost never need to deal with this in angular. ( And I think that is one of its strengths! ).
Here is a fiddle that solves the problem in a slightly different way.
http://jsfiddle.net/WJ226/5/
The controller is now simplified to
function VariousThingsCtrl($scope) {
$scope.students = students;
$scope.games = games;
$scope.remove = function (arrayName,$index) {
$scope[arrayName].splice($index,1);
}
}
Instead of passing the whole scope, why not just pass the $index ? Since you are already in the scope where the arrays are located, it should be pretty easy from then.
I have a basic application in AngularJS. The model contains a number of items and associated tags of those items. What I'm trying to achieve is the ability to filter the items displayed so that only those with one or more active tags are displayed, however I'm not having a lot of luck with figuring out how to manipulate the model from the view.
The JS is available at http://jsfiddle.net/Qxbka/2 . This contains the state I have managed to reach so far, but I have two problems. First off, the directive attempts to call a method toggleTag() in the controller:
template: "<button class='btn' ng-repeat='datum in data' ng-click='toggleTag(datum.id)'>{{datum.name}}</button>"
but the method is not called. Second, I'm not sure how to alter the output section's ng-repeat so that it only shows items with one or more active tags.
Any pointers on what I'm doing wrong and how to get this working would be much appreciated.
Update
I updated the method in the directive to pass the data items directly, i.e.
template: "<button class='btn' ng-repeat='datum in data' ng-click='toggle(data, datum.id)'>{{datum.name}}</button>"
and also created a toggle() method in the directive. By doing this I can manipulate data and it is reflected in the state HTML, however I would appreciate any feedback as to if this is the correct way to do this (it doesn't feel quite right to me).
Still stuck on how to re-evaluate the output when a tag's value is updated.
You can use a filter (docs) on the ng-repeat:
<li ng-repeat="item in items | filter:tagfilter">...</li>
The argument to the filter expression can be many things, including a function on the scope that will get called once for each element in the array. If it returns true, the element will show up, if it returns false, it won't.
One way you could do this is to set up a selectedTags array on your scope, which you populate by watching the tags array:
$scope.$watch('tags', function() {
$scope.selectedTags = $scope.tags.reduce(function(selected, tag) {
if (tag._active) selected.push(tag.name);
return selected;
}, []);
}, true);
The extra true in there at the end makes angular compare the elements by equality vs reference (which we want, because we need it to watch the _active attribute on each tag.
Next you can set up a filter function:
$scope.tagfilter = function(item) {
// If no tags are selected, show all the items.
if ($scope.selectedTags.length === 0) return true;
return intersects($scope.selectedTags, item.tags);
}
With a quick and dirty helper function intersects that returns the intersection of two arrays:
function intersects(a, b) {
var i = 0, len = a.length, inboth = [];
for (i; i < len; i++) {
if (b.indexOf(a[i]) !== -1) inboth.push(a[i]);
}
return inboth.length > 0;
}
I forked your fiddle here to show this in action.
One small issue with the way you've gone about this is items have an array of tag "names" and not ids. So this example just works with arrays of tag names (I had to edit some of the initial data to make it consistent).