[$injector:modulerr] Failed to instantiate module due to an error

The [$injector:modulerr] error in AngularJS occurs when the app fails to load a module due to issues such as:

• Missing dependencies
• Incorrect module definitions
• Syntax errors in module files

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1. Understanding the [$injector:modulerr] Error

When AngularJS initializes, it looks for all declared modules and their dependencies. If it fails to find or load any module, it throws the [$injector:modulerr] error.

Error Example in Console:

[$injector:modulerr] Failed to instantiate module myApp due to:
Error: [$injector:modulerr] Failed to instantiate module myDependency due to:
Error: [$injector:nomod] Module 'myDependency' is not available!

What this means:

• myApp depends on myDependency, but AngularJS cannot find myDependency.

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2. Common Causes & Fixes

1. Missing Dependency in angular.module()

Issue:
The module dependency is missing in the angular.module declaration.

Incorrect Code:

angular.module('myApp', []); // Missing 'myDependency'

Fix:
Ensure all dependencies are included:

angular.module('myApp', ['myDependency']);

Check that myDependency is defined correctly before using it.

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2. Module Not Loaded in script Tag

Issue:
The dependency module is not included in the HTML file.

Incorrect Code (Missing Script):

<script src="angular.min.js"></script>
<script src="app.js"></script> <!-- 'myDependency' is missing -->

Fix:
Include all module scripts before the main app file:

<script src="angular.min.js"></script>
<script src="myDependency.js"></script>  <!-- Add dependency module -->
<script src="app.js"></script>

Ensure correct order of scripts! The dependency must be loaded before the main app.

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3. Typo in Module Name

Issue:
The module name is spelled incorrectly in angular.module().

Incorrect Code:

angular.module('myApp', ['MyDependency']); // Wrong casing

Fix:
Ensure the module name matches exactly:

angular.module('myApp', ['myDependency']); // Correct name

AngularJS module names are case-sensitive.

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4. ng-app Defined Incorrectly

Issue:
If the ng-app directive is missing or does not match the module name, AngularJS won’t bootstrap the app.

Incorrect Code:

<div ng-app="wrongAppName">  <!-- Mismatched name -->

Fix:
Ensure the ng-app directive matches the module name:

<div ng-app="myApp">

---

5. Circular Dependency Between Modules

Issue:
Modules depend on each other, causing a circular dependency.

Incorrect Code (Circular Dependency):

angular.module('moduleA', ['moduleB']);
angular.module('moduleB', ['moduleA']);

What happens?

• moduleA requires moduleB, but moduleB also requires moduleA, causing an infinite loop.

Fix:
Avoid circular dependencies. If needed, use services instead of direct dependencies.

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6. angular.module() Called More Than Once for the Same Module

Issue:
Calling angular.module('myApp', []) twice redefines the module, causing conflicts.

Incorrect Code:

angular.module('myApp', []);  // First definition
angular.module('myApp', []);  // Overwrites the first one!

Fix:
Use .module('myApp') without redefining it.

angular.module('myApp', []);  // Define only once
angular.module('myApp');      // Access existing module

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7. Module File Contains Syntax Errors

Issue:
If a JavaScript file has a syntax error, the module fails to load.

Example Error (Syntax Mistake):

angular.module('myApp', [
    'dependency1',
    'dependency2' // Missing comma here
    'dependency3'
]);

Fix:
Ensure correct syntax:

angular.module('myApp', [
    'dependency1',
    'dependency2',
    'dependency3'
]);

Check the browser console for syntax errors!

---

8. Using AngularJS 1.x Syntax with Angular 2+

Issue:
If an AngularJS module (angular.module()) is used in an Angular 2+ app, it will fail.

Incorrect Usage in Angular 2+:

angular.module('myApp', []); // Angular 2+ does not use this!

Fix:
In Angular 2+, use NgModule instead of angular.module():

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

@NgModule({
  declarations: [],
  imports: [],
  providers: [],
  bootstrap: []
})
export class AppModule { }

If you’re migrating, use ngUpgrade to run both frameworks together.

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3. Debugging the Error in Chrome DevTools

Step 1: Open DevTools Console

1. Right-click on the page and select Inspect
2. Go to the Console tab
3. Look for [$injector:modulerr] errors

Step 2: Identify the Missing Module
The error message will tell you which module is missing:

Error: [$injector:modulerr] Failed to instantiate module 'myApp' due to:
Error: [$injector:nomod] Module 'myDependency' is not available!

➡ Fix: Ensure myDependency.js is loaded before app.js.

Step 3: Check Network Requests

1. Go to the Network tab in Chrome DevTools
2. Look for 404 errors on missing module files

Step 4: Use angular.module('myApp') in the Console
Run this in the browser console to check if the module exists:

angular.module('myApp');

If it throws an error, the module is not loaded correctly.