Uncaught Error: Encountered undefined provider

Hi Guys,

Here is how you can fix the issue "Uncaught Error: Encountered undefined provider" . Have a look at the stack trace below.


compiler.js:485 

Uncaught Error: Encountered undefined provider! Usually this means you have a circular dependencies (might be caused by using 'barrel' index.ts files.
    at syntaxError (compiler.js:485)
    at eval (compiler.js:15725)
    at Array.forEach (<anonymous>)
    at CompileMetadataResolver._getProvidersMetadata (compiler.js:15710)
    at CompileMetadataResolver.getNonNormalizedDirectiveMetadata (compiler.js:14994)
    at CompileMetadataResolver._getEntryComponentMetadata (compiler.js:15812)
    at eval (compiler.js:15293)
    at Array.map (<anonymous>)
    at CompileMetadataResolver.getNgModuleMetadata (compiler.js:15293)
    at JitCompiler._loadModules (compiler.js:34226)


To find out which part of the code is throwing  this error , first have a check in the component.ts file.
Check the value of provider attribute in the @Component decorator .

Invalid providers for "AppComponent" - only instances of Provider and Type are allowed

Hi Guys,

You might have faced the issue "Invalid providers for "AppComponent" - only instances of Provider and Type are allowed" .

The full stack trace is as below:

Uncaught Error: Invalid providers for "AppComponent" - only instances of Provider and Type are allowed, got: [?./user.service.ts?]
    at syntaxError (webpack-internal:///../../../compiler/esm5/compiler.js:706)
    at eval (webpack-internal:///../../../compiler/esm5/compiler.js:15963)
    at Array.forEach (<anonymous>)
    at CompileMetadataResolver._getProvidersMetadata (webpack-internal:///../../../compiler/esm5/compiler.js:15931)
    at CompileMetadataResolver.getNonNormalizedDirectiveMetadata (webpack-internal:///../../../compiler/esm5/compiler.js:15215)
    at CompileMetadataResolver._getEntryComponentMetadata (webpack-internal:///../../../compiler/esm5/compiler.js:16033)
    at eval (webpack-internal:///../../../compiler/esm5/compiler.js:15514)
    at Array.map (<anonymous>)
    at CompileMetadataResolver.getNgModuleMetadata (webpack-internal:///../../../compiler/esm5/compiler.js:15514)
    at JitCompiler._loadModules (webpack-internal:///../../../compiler/esm5/compiler.js:34447)



To find the root cause of the issue first check the providers attribute of @Component decorator in the component.ts file.

If the value is anything other than a valid Typescript type you will get the above error.

property binding in Angular 5

Hi Guys,

Let's understand what is property binding in angular 5.

We all know that an HTML element has various properties like id , name , value, etc. . Angular provides a way to bind to the property of HTML elements , called property binding .

There are multiple use cases that can be simplified using property binding like , if you have to change the value of a text field dynamically , or enable/disable a button. Let's see how can we do it.

First create an html file which will act as a component . Name this file as test.component.html , in this file have a text field . To bind a property we need to put the property in []. Here we are going to bind the value property , so I have placed value in square brackets . Since I am going to bind this property to a dynamic value , I will do so by assigning the property to a variable myValue.

<input type="text" [value]="myValue">

You need to define myValue in the component file . So , create a typescript file and name it as test.component.ts . The content of the file should be as below.

import { Component } from '@angular/core';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html'
})
export class TestComponent {
myValue="test";
}

Finally update your index.html as 

<app-test></app-test>

That's all , verify the code by refreshing the localhost:4200 in chrome browser . You will see the output as

---

node_modules appears empty, you may need to run 'npm install'

Hi Guys,


You might face the error node_modules appears empty, you may need to run 'npm install'  if you try to test an angular 2/4/5 application . 

node_modules appears empty, you may need to run 'npm install'

This error occurs when you use the command ng serve.

C:\projects\my-app> ng serve

Note that this command is used to start a server , serving the angular application .

The most common cause of this error is missing node_modules folder in the directory from which you have called ng serve.

To solve this take the following steps.

1. Check , if you have called ng serve from the correct location ? to serve the application you need to navigate to the project folder and then call ng serve .

2. If you are in correct folder , check if you have a folder named node_modules in it.If not your project is incomplete . Create a new application using ng new and replace the src folder of new app with src folder of your existing app.

C:\projects> ng new my-app-new

Copy the src folder in my-app to my-app-new

C:\projects> cd my-app-new
C:\projects\my-app-new> ng serve

3. If you have node_modules  folder available and in your app folder then it might be corrupted. To solve this create a new application using ng new and replace the src folder of new app with src folder of your existing app.


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