Added .d.ts file, so lib can be used in typescript react-native projects

index.d.ts

@@ -0,0 +1,41 @@
+// Module d.ts file
+
+// Enables using module in typescript react-native projects,
+// with editor auto-complete and type-validation (in VS Code)
+
+// See:
+// Typescript docs:
+//   https://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-d-ts.html
+// Typescript Playground, for automatic generation of .d.ts file from .js:
+//   https://www.typescriptlang.org/play?filetype=js&useJavaScript=true#code/Q
+// Simplest approach:
+// https://stackoverflow.com/a/51355583
+
+declare module "react-native-barometer";
+
+interface BarometerPayload {  // See module README for field descriptions
+  timestamp:number,
+  pressure:number,
+  altitudeASL:number,
+  altitude:number,
+  relativeAltitude:number,
+  verticalSpeed:number,
+};
+
+type BarometerWatchCallbackFn = (payload:BarometerPayload) => void;
+
+declare namespace Barometer {  // See module README for function descriptions
+  function isSupported(): Promise<boolean>;
+  function setInterval(interval: number): void;
+  function setLocalPressure(pressure: number): void;
+  function watch(success: BarometerWatchCallbackFn): number;
+  function clearWatch(watchID: any): void;
+  function stopObserving(): void;
+}
+
+export {
+  BarometerPayload,
+  BarometerWatchCallbackFn
+};
+
+export default Barometer;