Ngfor angular

In this example, we are creating ngfor angular item using the let keyword of the friendlist array. It will iterate over each item in the array, and will print out the item name and item age, or any other object key we have in the array object, ngfor angular.

NgFor is a structural directive, meaning that it changes the structure of the DOM. Sometimes we also want to get the index of the item in the array we are iterating over. We can do this by adding another variable to our ngFor expression and making it equal to index , like so:. If our data structure was in fact grouped by country we can use two ngFor directives, like so:. We use the NgFor directive to loop over an array of items and create multiple elements dynamically from a template element. We can get the index of the item we are looping over by assigning index to a variable in the NgFor expression. Learning Objectives Know how to use the NgFor directive in your application.

Ngfor angular

In this post we are going to go over the ngFor core directive, namely we are going to go over the following:. So let's get started diving into ngFor! Below you can also find a video version of this post if you prefer, and the running code of this post is available here. Note: If instead of ngIf you are looking for the for syntax, then check my other guide instead: Angular for: Complete Guide. The core directive ngFor allows us to build data presentation lists and tables in our HTML templates. Let's take for example the following data:. With ngFor we can print this data to the screen under the form of a data table, by generating HTML similar to this:. This template will generate the HTML table that we showed just above. We can see in this example the most common syntax for using ngFor :. Note that the loop variable hero is only visible inside the loop, you would not be able to access it outside the ngFor section. If you have an AngularJs background, you will see this error a few times before you get used to the new Angular syntax:. This is because you have accidentally either used item in items instead of item of items , or forgot to add the let keyword at the beginning of the expression:. A very common requirement is to add to a list the numeric index position of its element. We can get the index of the current element by using the index variable:.

Another very common functionality needed when building tables is to be able to stripe a table by adding a different css class to the even ngfor angular odd rows. In order to so, we have a couple of variables available for that: even and oddthat can be used in the following way together with ngClass : Let's have a look at the HTML generated by this template: As we can see, ngClass added the CSS classes to the right out-file powershell, as we would expect, ngfor angular. This will change the value of hideList to false from true.

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The NgFor directive instantiates a template once per item from an iterable. The context for each instantiated template inherits from the outer context with the given loop variable set to the current item from the iterable. Angular uses object identity to track insertions and deletions within the iterator and reproduce those changes in the DOM. Inserted rows can be animated in, deleted rows can be animated out, and unchanged rows retain any unsaved state such as user input. It is possible for the identities of elements in the iterator to change while the data does not. Even if the data hasn't changed, the second response will produce objects with different identities, and Angular will tear down the entire DOM and rebuild it as if all old elements were deleted and all new elements inserted. This is an expensive operation and should be avoided if possible. To customize the default tracking algorithm, NgFor supports trackBy option. If trackBy is given, Angular tracks changes by the return value of the function.

Ngfor angular

In this example, we are creating an item using the let keyword of the friendlist array. It will iterate over each item in the array, and will print out the item name and item age, or any other object key we have in the array object. You will see the above output when you save.

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It will iterate over each item in the array, and will print out the item name and item age, or any other object key we have in the array object. This is because you have accidentally either used item in items instead of item of items , or forgot to add the let keyword at the beginning of the expression:. Note that you need the let keyword to get the value of the index, otherwise you will get an error similar to this one:. If that happens to be the case, we can configure ngFor to do the tracking by something else other than object identity. This is the case if for example we query the data again from the backend. In this example, we are creating an item using the let keyword of the friendlist array. I build projects to learn how code works. We can get the index of the current element by using the index variable:. If you read this far, thank the author to show them you care. I hope you enjoyed the post, I invite you to have a look at the list below for other similar posts and resources on Angular. Also, create a function called hideList that will change the value of isVisible to false if triggered. So, we we get 8 items in our list tag. This will change the value of hideList to false from true.

We will discover, how we can use the ngFor directive to display multiple elements directly from a JavaScript array.

This will add a CSS class named first to the first element of the list, and a CSS class named last to the last element of the list:. Note This directive is the successor of Angular 1s ng-repeat directive. As we see, ngFor already does a lot of optimizations out-of-the-box to try to reuse existing DOM elements as much as possible, but it's doing so based on object identity. To illustrate this, we are going to define a directive for a configuration element called hero : We can now use this configuration element in our template in the following way: Now let's query this data from the configuration elements using ContentChildren : Do you see what happened here? Note The index is always zero based, so starts at 0 then 1,2,3,4 etc…. Just like the even and odd functionality, there are also two other variables that can be used to identify the first and the last elements of the list:. This is the case if for example we query the data again from the backend. And the same could be done with any other Iterable in our program. Why can this be important for performance? Tracking by object identity is a good default strategy because Angular has no information about the object so it cannot tell which property it should use for tracking. So, in this example, we are showing the list in a different format. Get started.