Fix constructor init (#774)

* Update test app to RN 0.39.0

* Fix getContext in index.js

* Add dependency on invariant

* Add some comments to getContext

* Make invariant a devdependency rather than a dependency

lib/index.js

@@ -25,30 +25,40 @@ function nodeRequire(module) {
 
 
 function getContext() {
+    // If process is an object, we're probably running in Node or Electron
+    // From: http://stackoverflow.com/a/24279593/1417293
     if (typeof process === 'object' && process + '' === '[object process]') {
         return process.type === 'renderer' ? 'electron' : 'nodejs';
-    }        
+    }
 
-    if (typeof navigator !== 'undefined') {
-        if (navigator.product === 'ReactNative') { // eslint-disable-line no-undef
+    // When running via Jest, the jest object is defined.
+    if (typeof jest === 'object') {
+        return 'nodejs';
+    }
+
+    // If we've already injected the Realm class, we are probably
+    // running in a jscore environment, either directly or via React Native
+    if (typeof Realm !== 'undefined') {
+        if (typeof navigator !== 'undefined' && 
+            navigator.product === 'ReactNative') { // eslint-disable-line no-undef
             return 'reactnative';
         }
 
-        if (/Chrome/.test(navigator.userAgent)) { // eslint-disable-line no-undef
-            return 'chromedebugger';
-        }
-    }
-
-    if (typeof global !== 'undefined') {
-        if (global.__debug__) {
-            return 'vscodedebugger';
-        }
-    }
-
-    if (typeof Realm !== 'undefined') {
         return 'jscore';
     }
 
+    // Visual Studio Code defines the global.__debug__ object.
+    if (typeof global !== 'undefined' && global.__debug__) {
+        return 'vscodedebugger';
+    }
+
+    // Finally, if the navigator.userAgent contains the string "Chrome", we're likely
+    // running via the chrome debugger.
+    if (typeof navigator !== 'undefined' && 
+        /Chrome/.test(navigator.userAgent)) { // eslint-disable-line no-undef
+        return 'chromedebugger';
+    }
+
     throw Error("Unknown execution context");
 }
 

tests/react-test-app/package.json

@@ -6,11 +6,14 @@
     "start": "react-native start"
   },
   "dependencies": {
-    "react": "15.3.2",
-    "react-native": "^0.37.0",
+    "react": "15.4.0",
+    "react-native": "^0.39.0",
     "react-native-fs": "^1.1.0",
     "realm": "file:../..",
     "realm-tests": "file:../js",
     "xmlbuilder": "^4.2.1"
+  },
+  "devDependencies": {
+    "invariant": "^2.2.2"
   }
 }