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Questions tagged [angular]

Questions about Angular (not to be confused with AngularJS), the web framework from Google. Use this tag for Angular questions which are not specific to an individual version. For the older AngularJS (1.x) web framework, use the AngularJS tag.

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2142 votes
52 answers
1.7m views

Can't bind to 'ngModel' since it isn't a known property of 'input'

I have this simple input in my component which uses [(ngModel)] : <input type="text" [(ngModel)]="test" placeholder="foo" /> And I get the following error when I ...
Anthony Brenelière's user avatar
1883 votes
35 answers
843k views

What is the difference between Promises and Observables?

What is the difference between Promise and Observable in Angular? An example on each would be helpful in understanding both the cases. In what scenario can we use each case?
Rohit's user avatar
  • 18.9k
1497 votes
28 answers
851k views

Difference between Constructor and ngOnInit

Angular provides life cycle hook ngOnInit by default. Why should ngOnInit be used, if we already have a constructor?
Haseena P A's user avatar
  • 17.2k
1348 votes
52 answers
1.5m views

Can't bind to 'formGroup' since it isn't a known property of 'form'

The situation I am trying to make what should be a very simple form in my Angular application, but no matter what, it never works. The Angular version Angular 2.0.0 RC5 The error Can't bind to '...
FrancescoMussi's user avatar
1209 votes
24 answers
2.2m views

Angular: conditional class with *ngClass

What is wrong with my Angular code? I am getting the following error: Cannot read property 'remove' of undefined at BrowserDomAdapter.removeClass <ol> <li *ngClass="{active: step==='...
daniel's user avatar
  • 35.2k
1088 votes
25 answers
751k views

Angular HTML binding

I am writing an Angular application and I have an HTML response I want to display. How do I do that? If I simply use the binding syntax {{myVal}} it encodes all HTML characters (of course). I need ...
Aviad P.'s user avatar
  • 32.4k
1054 votes
28 answers
432k views

Angular/RxJS When should I unsubscribe from `Subscription`

When should I store the Subscription instances and invoke unsubscribe() during the ngOnDestroy life cycle and when can I simply ignore them? Saving all subscriptions introduces a lot of mess into ...
Sergey Tihon's user avatar
  • 12.6k
1032 votes
14 answers
679k views

What is the difference between BehaviorSubject and Observable?

I'm looking into the design patterns of RxJS, and I do not understand the difference between BehaviorSubject and Observable. From my understanding, BehaviorSubject can contain a value that may change. ...
Kevin Mark's user avatar
  • 10.4k
1010 votes
25 answers
1.4m views

How can I use "*ngIf else"?

I'm using Angular and I want to use *ngIf else (available since version 4) in this example: <div *ngIf="isValid"> content here ... </div> <div *ngIf="!isValid">...
El houcine bougarfaoui's user avatar
963 votes
39 answers
1.3m views

Property '...' has no initializer and is not definitely assigned in the constructor

in my Angular app i have a component: import { MakeService } from './../../services/make.service'; import { Component, OnInit } from '@angular/core'; @Component({ selector: 'app-vehicle-form', ...
Mikhail Kostiuchenko's user avatar
928 votes
11 answers
1.7m views

ngFor with index as value in attribute

I have a simple ngFor loop which also keeps track of the current index. I want to store that index value in an attribute so I can print it. But I can't figure out how this works. I basically have ...
Vivendi's user avatar
  • 20.7k
895 votes
49 answers
1.8m views

Angular 6 - Could not find module "@angular-devkit/build-angular"

After updating to Angular 6.0.1, I get the following error on ng serve: Could not find module "@angular-devkit/build-angular" from "/home/Projects/myProjectName". Error: Could not ...
ForestG's user avatar
  • 17.9k
875 votes
22 answers
682k views

How to detect when an @Input() value changes in Angular?

I have a parent component (CategoryComponent), a child component (videoListComponent) and an ApiService. I have most of this working fine i.e. each component can access the json api and get its ...
Jon Catmull's user avatar
  • 12.6k
770 votes
36 answers
1.6m views

Unable to resolve dependency tree error when installing npm packages

When trying to install the npm packages using npm i command, I am getting the following exception: I have tried reinstalling the Node.js package and setting the proxy to off using: set HTTP_PROXY= ...
Pearl's user avatar
  • 9,099
766 votes
44 answers
1.2m views

How to get current route

The current docs only talk about getting route params, not the actual route segments. For example, if i want to find the parent of current route, how is that possible?
pdeva's user avatar
  • 44.8k
749 votes
30 answers
993k views

No provider for HttpClient

After upgrading from angular 4.4 to 5.0 and after updating all HttpModule and Http to HttpClientModule I started to get this error. I also added HttpModule again to be sure it's not due to some ...
Himmet Yelekin's user avatar
748 votes
23 answers
860k views

What is the equivalent of ngShow and ngHide in Angular 2+?

I have a number of elements that I want to be visible under certain conditions. In AngularJS I would write <div ng-show="myVar">stuff</div> How can I do this in Angular 2+?
Mihai Răducanu's user avatar
744 votes
15 answers
990k views

How can I select an element in a component template?

Does anybody know how to get hold of an element defined in a component template? Polymer makes it really easy with the $ and $$. I was just wondering how to go about it in Angular. Take the example ...
Aman Gupta's user avatar
  • 8,063
690 votes
21 answers
766k views

access key and value of object using *ngFor

I am a bit confused about how to get the key and value of an object in angular2 while using *ngFor for iterating over the object. I know in angular 1.x there is a syntax like ng-repeat="(key, value) ...
Pardeep Jain's user avatar
  • 86.1k
680 votes
31 answers
755k views

How to detect a route change in Angular?

I am looking to detect a route change in my AppComponent. Thereafter I will check the global user token to see if the user is logged in so that I can redirect the user if the user is not logged in.
AngularM's user avatar
  • 16.5k
662 votes
4 answers
118k views

What is the meaning of the "at" (@) prefix on npm packages?

In the Angular Component Router documentation I just stumbled over a npm command I have never seen before and I don't understand what is going on: npm install @angular/router --save What is the ...
jbandi's user avatar
  • 18k
652 votes
19 answers
493k views

*ngIf and *ngFor on same element causing error

I'm having a problem with trying to use Angular's *ngFor and *ngIf on the same element. When trying to loop through the collection in the *ngFor, the collection is seen as null and consequently ...
garethdn's user avatar
  • 12.3k
645 votes
14 answers
66k views

Huge number of files generated for every Angular project

I wanted to start a simple hello world app for Angular. When I followed the instructions in the official quickstart the installation created 32,000 files in my project. I figured this is some ...
Moshe Shaham's user avatar
  • 15.7k
627 votes
6 answers
542k views

WARNING in budgets, maximum exceeded for initial

When building my Angular 7 project with --prod, I receive a warning in budgets. I have an Angular 7 project. I am trying to build it, but I keep getting the following warning: WARNING in budgets, ...
Masoud Bimar's user avatar
  • 7,561
589 votes
27 answers
618k views

How to go back last page

Is there a smart way to go back last page in Angular 2? Something like this._router.navigate(LASTPAGE); For example, page C has a Go Back button, Page A -> Page C, click it, back to page A. Page B ...
Hongbo Miao's user avatar
  • 48.6k
573 votes
31 answers
538k views

ExpressionChangedAfterItHasBeenCheckedError Explained

Please explain to me why I keep getting this error: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Obviously, I only get it in dev mode, it doesn't happen ...
Kevin LeStarge's user avatar
571 votes
24 answers
622k views

Error: More than one module matches. Use skip-import option to skip importing the component into the closest module

When I try to create a component in the angular cli, it's showing me this error. How do I get rid of it ? Error: More than one module matches. Use skip-import option to skip importing the component ...
Anamul Haque's user avatar
  • 7,249
563 votes
11 answers
377k views

Can't bind to 'formControl' since it isn't a known property of 'input' - Angular2 Material Autocomplete issue

I am trying to use Angular Material Autocomplete component in my Angular 2 project. I added the following to my template. <md-input-container> <input mdInput placeholder="Category" [...
Lahiru Chandima's user avatar
557 votes
12 answers
169k views

@Directive vs @Component in Angular

What is the difference between @Component and @Directive in Angular? Both of them seem to do the same task and have the same attributes. What are the use cases and when to prefer one over another?
Prasanjit Dey's user avatar
552 votes
28 answers
759k views

how to reset <input type = "file"> in Angular

I am developing a metro app with VS2012 and Javascript I want to reset the contents of my file input: <input type="file" id="uploadCaptureInputFile" class="win-content colors" accept="image/*" /&...
Jesus's user avatar
  • 8,506
546 votes
16 answers
717k views

Binding select element to object in Angular

I'd like to bind a select element to a list of objects -- which is easy enough: @Component({ selector: 'myApp', template: `<h1>My Application</h1> <select [(ngModel)]...
RHarris's user avatar
  • 11k
533 votes
6 answers
210k views

What is the difference between declarations, providers, and import in NgModule?

I am trying to understand Angular (sometimes called Angular2+), then I came across @Module: Imports Declarations Providers Following Angular Quick Start
Ramesh Papaganti's user avatar
520 votes
6 answers
1.1m views

(change) vs (ngModelChange) in angular

Angular 1 does not accept onchange() event, it's only accepts ng-change() event. Angular 2, on the other hand, accepts both (change) and (ngModelChange) events, which both seems to be doing the same ...
Ramesh Rajendran's user avatar
513 votes
43 answers
771k views

mat-form-field must contain a MatFormFieldControl

We are trying to build our own form-field-Components at our Company. We are trying to wrap material design's Components like this: field: <mat-form-field> <ng-content></ng-content&...
Viktor Eriksson's user avatar
511 votes
14 answers
874k views

How can I get new selection in "select" in Angular 2?

I am using Angular 2 (TypeScript). I want to do something with the new selection, but what I get in onChange() is always the last selection. How can I get the new selection? <select [(ngModel)]="...
Hongbo Miao's user avatar
  • 48.6k
509 votes
49 answers
476k views

Error when trying to inject a service into an angular component "EXCEPTION: Can't resolve all parameters for component", why?

I've built a basic app in Angular, but I have encountered a strange issue where I cannot inject a service into one of my components. It injects fine into any of the three other components I have ...
Keith Otto's user avatar
  • 5,148
496 votes
4 answers
414k views

Triggering change detection manually in Angular

I'm writing an Angular component that has a property Mode(): string. I would like to be able to set this property programmatically not in response to any event. The problem is that in the absence of ...
jz87's user avatar
  • 9,437
488 votes
12 answers
220k views

Angular exception: Can't bind to 'ngForIn' since it isn't a known native property

What am I doing wrong? import {bootstrap, Component} from 'angular2/angular2' @Component({ selector: 'conf-talks', template: `<div *ngFor="let talk in talks"> {{talk.title}} by {{talk....
Mark Rajcok's user avatar
482 votes
29 answers
284k views

Angular 2 Scroll to top on Route Change

In my Angular 2 app when I scroll down a page and click the link at the bottom of the page, it does change the route and takes me to the next page but it doesn't scroll to the top of the page. As a ...
Naveed Ahmed's user avatar
  • 10.3k
468 votes
9 answers
387k views

Angular - Use pipes in services and components

In AngularJS, I am able to use filters (pipes) inside of services and controllers using syntax similar to this: $filter('date')(myDate, 'yyyy-MM-dd'); Is it possible to use pipes in services/...
POSIX-compliant's user avatar
462 votes
10 answers
327k views

What is the difference between Subject and BehaviorSubject?

I'm not clear on the difference between a Subject and a BehaviorSubject. Is it just that a BehaviorSubject has the getValue() function?
Mike Jerred's user avatar
  • 10.3k
451 votes
23 answers
511k views

Expression ___ has changed after it was checked

Why is the component in this simple plunk @Component({ selector: 'my-app', template: `<div>I'm {{message}} </div>`, }) export class App { message:string = 'loading :('; ...
drew moore's user avatar
  • 32.3k
439 votes
19 answers
503k views

Property 'value' does not exist on type 'EventTarget'

I am using TypeScript Version 2 for an Angular 2 component code. I am getting error "Property 'value' does not exist on type 'EventTarget'" for below code, what could be the solution. Thanks!...
user584018's user avatar
430 votes
13 answers
773k views

Angular 2 change event on every keypress

The change event is only called after the focus of the input has changed. How can I make it so that the event fires on every keypress? <input type="text" [(ngModel)]="mymodel" (change)="...
daniel's user avatar
  • 35.2k
430 votes
3 answers
573k views

Can't bind to 'ngIf' since it isn't a known property of 'div' [duplicate]

Can't bind to 'ngIf' since it isn't a known property of 'div'. The element is <div [ngIf]="isAuth" id="sidebar"> And the component is: import SessionService from '../session/...
Ivaylo Ivanov's user avatar
427 votes
9 answers
382k views

Convert Promise to Observable

I am trying to wrap my head around observables. I love the way observables solve development and readability issues. As I read, benefits are immense. Observables on HTTP and collections seem to be ...
Krishnan Sriram's user avatar
426 votes
22 answers
898k views

How do I pass data to Angular routed components?

In one of my Angular 2 routes's templates (FirstComponent) I have a button first.component.html <div class="button" click="routeWithData()">Pass data and route</div> My goal is to ...
dragonmnl's user avatar
  • 15.2k
417 votes
21 answers
426k views

How to style child components from parent component's CSS file?

I've got a parent component: <parent></parent> And I want to populate this group with child components: <parent> <child></child> <child></child> <...
Chrillewoodz's user avatar
  • 27.9k
415 votes
19 answers
206k views

@ViewChild in *ngIf

Question What is the most elegant way to get @ViewChild after corresponding element in template was shown? Below is an example. Also Plunker available. Component.template.html: <div id="layout&...
sinedsem's user avatar
  • 5,633
415 votes
26 answers
642k views

How to use jQuery with Angular?

Can anyone tell me, how to use jQuery with Angular? class MyComponent { constructor() { // how to query the DOM element from here? } } I'm aware there are workarounds like ...
Waog's user avatar
  • 7,217

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