Decouple MapInstanceManager from window.farmOS.map

**Why?** Better support alternative bundling strategies
and scenarios where having mutable state in the global
`window.farmOS.map` is ugly/limiting.

These changes should allow farmOS-map to also be used
as follows;

```sh
npm install @farmos.org/farmos-map@2
```

```js
import MapInstanceManager from '@farmos.org/farmos-map/MapInstanceManager';

const maps = new MapInstanceManager();

const map = maps.create('my-map');
```

Some background can be found in the following issues;

* #113
* #68

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Remove redundant `defaults.behaviors` in favor of existing `farmOS.map.behaviors` mechanism for specifying the default behaviors.
 - Make instance behavior methods `async`.
 - Lazily load behaviors as separate Webpack chunks.
+- Decouple map instance creation/management from `window.farmOS.map`.
 
 ### Fixed
 

package.json

@@ -7,6 +7,7 @@
     "type": "git",
     "url": "https://github.com/farmOS/farmOS-map.git"
   },
+  "main": "src/index.js",
   "scripts": {
     "lint": "eslint src",
     "build": "npm run lint && webpack --config webpack.config.js --mode production",

src/MapInstanceManager.js

@@ -0,0 +1,65 @@
+// Import farmOS map instance factory function.
+import createInstance from './instance/instance';
+
+// Import farmOS-map CSS.
+import './styles.css';
+
+import namedBehaviors from './behavior';
+
+
+class MapInstanceManager {
+
+  constructor() {
+
+    // Initialize an array of farmOS map instances.
+    this.instances = [];
+
+    // Behaviors which can be added on-demand by name via `instance.addBehavior`
+    // These are objects with an attach() method that will be called when a map is
+    // created. They receive the instance object so that they can perform
+    // modifications to the map using instance methods.
+    this.namedBehaviors = { ...namedBehaviors };
+
+    // Map behaviors which will be automatically attached to all created map
+    // instances.
+    this.behaviors = {
+      rememberLayer: namedBehaviors.rememberLayer,
+    };
+
+  }
+
+  // Create a new farmOS map attached to a target element ID and add it to the
+  // global instances array.
+  create(target, options) {
+    const instance = createInstance({ target, options });
+
+    instance.instanceManager = this;
+
+    // Add the instance to the array.
+    this.instances.push(instance);
+
+    // Attach behaviors from farmOS.map.behaviors to the instance in order of weight - if any.
+    instance.defaultBehaviorsAttached = instance.attachBehaviorsByWeight(
+      Object.values(this.behaviors),
+    );
+
+    // Return the instance.
+    return instance;
+  }
+
+  // Destroy a farmOS map instance and remove it from the instances array.
+  destroy(target) {
+    const i = this.targetIndex(target);
+    if (i > -1) {
+      this.instances[i].map.setTarget(null);
+      this.instances.splice(i, 1);
+    }
+  }
+
+  // Look up an instance index based on its target element ID.
+  targetIndex(target) {
+    return this.instances.findIndex(instance => instance.target === target);
+  }
+}
+
+export default MapInstanceManager;

src/index.js

@@ -0,0 +1,2 @@
+/* eslint-disable-next-line import/prefer-default-export */
+export { default as MapInstanceManager } from './MapInstanceManager';

src/instance/methods/behavior.js

@@ -1,10 +1,8 @@
-import namedBehaviors from '../../behavior';
-
 /**
  * Add a behavior by name.
  */
 export async function addBehavior(name, options = {}) {
-  return this.attachBehavior(namedBehaviors[name], options);
+  return this.attachBehavior(this.instanceManager.namedBehaviors[name], options);
 }
 
 /**

src/main.js

@@ -1,62 +1,14 @@
-// Import farmOS map instance factory function.
-import createInstance from './instance/instance';
-
-import namedBehaviors from './behavior';
-
-// Import farmOS-map CSS.
-import './styles.css';
+import MapInstanceManager from './MapInstanceManager';
 
 // Define window.farmOS if it isn't already.
 if (typeof window.farmOS === 'undefined') {
   window.farmOS = {};
 }
 
-// Add a farmOS.map object that is available globaly.
-window.farmOS.map = {
-
-  // Initialize an array of farmOS map instances.
-  instances: [],
-
-  // Behaviors which can be added on-demand by name via `instance.addBehavior`
-  // These are objects with an attach() method that will be called when a map is
-  // created. They receive the instance object so that they can perform
-  // modifications to the map using instance methods.
-  namedBehaviors,
-
-  // Map behaviors which will be automatically attached to all created map
-  // instances.
-  behaviors: {
-    rememberLayer: namedBehaviors.rememberLayer,
-  },
+const INSTANCE = new MapInstanceManager();
 
-  // Create a new farmOS map attached to a target element ID and add it to the
-  // global instances array.
-  create(target, options) {
-    const instance = createInstance({ target, options });
-
-    // Add the instance to the array.
-    this.instances.push(instance);
-
-    // Attach behaviors from farmOS.map.behaviors to the instance in order of weight - if any.
-    instance.defaultBehaviorsAttached = instance.attachBehaviorsByWeight(
-      Object.values(this.behaviors),
-    );
-
-    // Return the instance.
-    return instance;
-  },
-
-  // Destroy a farmOS map instance and remove it from the instances array.
-  destroy(target) {
-    const i = this.targetIndex(target);
-    if (i > -1) {
-      this.instances[i].map.setTarget(null);
-      this.instances.splice(i, 1);
-    }
-  },
+// Add a farmOS.map object that is available globaly.
+window.farmOS.map = INSTANCE;
 
-  // Look up an instance index based on its target element ID.
-  targetIndex(target) {
-    return this.instances.findIndex(instance => instance.target === target);
-  },
-};
+// Export the default farmOS-map object
+export default INSTANCE;