How to create separate AngularJS controller files?

Using the angular.module API with an array at the end will tell angular to create a new module:

myApp.js

// It is like saying "create a new module"
angular.module('myApp.controllers', []); // Notice the empty array at the end here

Using it without the array is actually a getter function. So to seperate your controllers, you can do:

Ctrl1.js

// It is just like saying "get this module and create a controller"
angular.module('myApp.controllers').controller('Ctrlr1', ['$scope', '$http', function($scope, $http) {}]);

Ctrl2.js

angular.module('myApp.controllers').controller('Ctrlr2', ['$scope', '$http', function($scope, $http) {}]);

During your javascript imports, just make sure myApp.js is after AngularJS but before any controllers / services / etc...otherwise angular won't be able to initialize your controllers.

Although both answers are technically correct, I want to introduce a different syntax choice for this answer. This imho makes it easier to read what's going on with injection, differentiate between etc.

File One

// Create the module that deals with controllers
angular.module('myApp.controllers', []);

File Two

// Here we get the module we created in file one
angular.module('myApp.controllers')

// We are adding a function called Ctrl1
// to the module we got in the line above
.controller('Ctrl1', Ctrl1);

// Inject my dependencies
Ctrl1.$inject = ['$scope', '$http'];

// Now create our controller function with all necessary logic
function Ctrl1($scope, $http) {
  // Logic here
}

File Three

// Here we get the module we created in file one
angular.module('myApp.controllers')

// We are adding a function called Ctrl2
// to the module we got in the line above
.controller('Ctrl2', Ctrl2);

// Inject my dependencies
Ctrl2.$inject = ['$scope', '$http'];

// Now create our controller function with all necessary logic
function Ctrl2($scope, $http) {
  // Logic here
}

What about this solution? Modules and Controllers in Files (at the end of the page) It works with multiple controllers, directives and so on:

app.js

var app = angular.module("myApp", ['deps']);

myCtrl.js

app.controller("myCtrl", function($scope) { ..});

html

<script src="app.js"></script>
<script src="myCtrl.js"></script>
<div ng-app="myApp" ng-controller="myCtrl">

Google has also a Best Practice Recommendations for Angular App Structure I really like to group by context. Not all the html in one folder, but for example all files for login (html, css, app.js,controller.js and so on). So if I work on a module, all the directives are easier to find.

For brevity, here's an ES2015 sample that doesn't rely on global variables

// controllers/example-controller.js

export const ExampleControllerName = "ExampleController"
export const ExampleController = ($scope) => {
  // something... 
}

// controllers/another-controller.js

export const AnotherControllerName = "AnotherController"
export const AnotherController = ($scope) => {
  // functionality... 
}

// app.js

import angular from "angular";

import {
  ExampleControllerName,
  ExampleController
} = "./controllers/example-controller";

import {
  AnotherControllerName,
  AnotherController
} = "./controllers/another-controller";

angular.module("myApp", [/* deps */])
  .controller(ExampleControllerName, ExampleController)
  .controller(AnotherControllerName, AnotherController)

Not so graceful, but the very much simple in implementation solution - using global variable.

In the "first" file:

window.myApp = angular.module("myApp", [])
....

in the "second" , "third", etc:

myApp.controller('MyController', function($scope) {
    .... 
    });