We may receive a commission for purchases made through this link.This is an affiliate link. {{i}} I wanted to repeat particular element several amount of time, so I'm using *ngFor directive with hard-coded array like [1,2,3,4,5,6,7,8,9,10] and that got worked awesome.
It instantiates a template for every element of given iterator. Prior to this Angular 6.1 release we cannot iterate directly through objects key values & maps using *ngFor directive.. To tackle this issue Angular keyvalue pipe has been introduced. first: boolean: True when the item is the first item in the iterable. And display the index of ngFor element using angular expression.
Angular provides us with syntactic sugar syntax to ease their usage.The two most common error which can happen and consume lots of hours to realize they were so silly to make!We may some time face following error when using *ngFor directiveThis is a typo mistake we all do number of times because in the ng-repeat directive used to use in Angular js version 1 it was used like this In Angular applications, which use lazy-loading by having multiple modules for their own components, when we use To resolve this, you need to import the CommonModule in the submodule's So if you try to do something like above, it will throw a cute red error!
In that example, every second row has a slightly different color.Again, we can achieve that effect by assigning CSS-classes depending on the values:Now that we know the basics of ngFor, we are going to take a closer look at how it is working.One aspect of that, is to know, when changes are applied to the DOM.Well, first of all, manipulations to the DOM are quite expensive performance wise, compared to regular JavaScript code.Generally, re-rendering of the list occurs in one of three cases:To reduce DOM-manipulation to a bare minimum, angulars' ngFor directive is heavily optimized.For example, if a element is added to the array, it is not re-rendering the whole list. Well, actually it works quite the same way.With the statement "let element of array" we are defining a variable "element", that holds a reference to the current array element.Knowing that we can now add the persons' name and the age to each list element. I achieved what I wanted to do. You can iterate through the elements of a set in insertion order.
By default, it uses the reference of the object for that.Unfortunately, the default method of identifying objects by reference is quite limited in many cases. {{i}} Angular ngFor - Learn all Features including trackBy, why is it not only for Arrays? Angular provides NgForOf directive with ngFor selector. If the list is long or complex enough, this will increase the time it takes the browser to render updates. index: number: The index of the current item in the iterable. We can use the new Set object introduced in ECMAScript2015 with the ngFor directive. Hey all! This array could look like this example data:And we want the result to be generated HTML that could look like this:All we need to do is to tell the directive, which array to use.Let's say we have a component that we call example-component.That array could be static and look like the array above or could be filled at runtime.
Use the spread operator on the array's keys to populate the returned array with incrementing integer values.Note: If you are compiling to ES5 you will need to add this to your ; let i = index;">{{i}}
*ngFor is one of the most popular directives in Angular — however, if not used well, it may damage your app’s performance. Let's call it "i" for now.
Example 1: Demo.Component.ts But it is not impossible to do. Read more in ourThis is an affiliate link. This code is fine, but with Angular 2 we can do better. ... Now you’ve learned the basics of Angular’s NgFor it’s time to take things up a notch and introduce some Observables.
2. The ngFor directive does create the HTML-Element it is placed in as many times as there are elements in the array. A few examples of how to use *ngFor to repeat an element a specified number of times.
They are very fast when it comes to accessing data by a key.Unfortunately, we can't just use objects with ngFor.