AngularJS新手求助：实例化app模块失败，提示Module 'app'不可用

Hey there! I’ve been in your exact spot before—those module errors can drive you crazy even when you swear you didn’t misspell anything. Let’s walk through the most common, easy-to-miss fixes for these frustrating issues:

• Double-check your script load order
  AngularJS core library must load before your app module script. If you load your app.js first, the browser won’t recognize angular.module() yet. Here’s the correct order:

  <!-- Load AngularJS first -->
  <script src="angular.min.js"></script>
  <!-- Then load your app module file -->
  <script src="app.js"></script>
  

• Verify your module definition syntax
  Make sure you’re defining the module (not just trying to retrieve it) with the empty array parameter. This is a super common mistake:

  // ✅ Correct: Defines the 'app' module with no dependencies
  angular.module('app', []);
  
  // ❌ Wrong: Tries to get an existing 'app' module that doesn't exist yet
  angular.module('app');
  

• Check for duplicate module definitions
  If you’ve defined angular.module('app', []) in multiple files, the later definition will overwrite the earlier one—this can break dependencies or wipe out your module entirely. Stick to one module definition file.

• Ensure all dependency modules are loaded
  If your app module relies on other modules (like ngRoute or ngResource), make sure those scripts are loaded before your app module. For example:

  <script src="angular.min.js"></script>
  <script src="angular-route.min.js"></script>
  <script src="app.js"></script>
  

  And don’t forget to include the dependency in your module definition:

  angular.module('app', ['ngRoute']);
  

• Confirm the ng-app directive is correct
  Your root HTML element (usually <html> or <body>) needs ng-app="app", and it’s case-sensitive. If you wrote ng-app="App" instead, Angular won’t find your module.

• Clear browser cache
  Sometimes old, cached scripts are the culprit. Force a hard refresh (Ctrl+F5 on Windows/Linux, Cmd+Shift+R on Mac) or disable cache in your browser’s developer tools (check the "Disable cache" box in the Network tab).

These are the simple fixes that usually resolve these errors. If you’re still stuck, sharing your app.js code and the script loading section of your HTML would help narrow it down further!

内容的提问来源于stack exchange，提问作者M Masood