Add enable option

An `enable` option is added as a new third argument, which defaults to
`true`. It can be set to `false` to disable geolocation. The idea is
that the option can be flipped to `true` once the user has indicated
that they want to be geolocated.

This means the hook can be made conditional without violating the rules
of hooks and without a conditional nested component which would need to
pass its data back up the tree.

Closes #51

README.md

@@ -41,6 +41,14 @@ const ComponentWithGeolocation = () => {
 };
 ```
 
+### Disabling until the user has opted in
+
+You can pass `false` as the third argument to prevent geolocation.
+
+```jsx
+const geolocation = useGeolocation({}, () => {}, false);
+```
+
 ### Using `PositionOptions`
 
 [There is a way](https://developer.mozilla.org/en-US/docs/Web/API/Geolocation_API#Fine_tuning_response) to use `PositionOptions` to fine tune response coming from `watchPosition` of the Geolocation API.

src/index.d.ts

@@ -7,6 +7,7 @@ declare module "react-hook-geolocation" {
 
   export default function useGeolocation(
     positionOptions?: PositionOptions,
-    callback?: (geolocation: EnrichedGeolocationCoordinates) => void
+    callback?: (geolocation: EnrichedGeolocationCoordinates) => void,
+    enable?: boolean
   ): EnrichedGeolocationCoordinates;
 }

src/index.js

@@ -2,7 +2,8 @@ import { useEffect, useState, useCallback } from "react";
 
 const useGeolocation = (
   { enableHighAccuracy, maximumAge, timeout } = {},
-  callback
+  callback,
+  enable = true
 ) => {
   const [coordinates, setCoordinates] = useState({
     accuracy: null,
@@ -72,6 +73,8 @@ const useGeolocation = (
   }, []);
 
   useEffect(() => {
+    if (!enable) return;
+
     let watchId;
 
     if (navigator.geolocation) {
@@ -93,6 +96,7 @@ const useGeolocation = (
       }
     };
   }, [
+    enable,
     callback,
     enableHighAccuracy,
     maximumAge,

src/index.test.js

@@ -24,10 +24,42 @@ const errorHandler = (data) => (_, onError) => {
 };
 
 describe("useGeolocation", () => {
+  beforeEach(() => {
+    jest.resetAllMocks();
+  });
+
   describe("when geolocation data is available", () => {
-    beforeEach(() => {
-      mockCallback.mockReset();
-      mockClearWatch.mockReset();
+    it("does nothing if the enable switch is false", () => {
+      const mockCoordinates = {
+        latitude: 12.3456789,
+        longitude: 34.5678912,
+        altitude: null,
+        accuracy: 12.345,
+        altitudeAccuracy: null,
+        heading: null,
+        speed: null,
+      };
+      mockGetCurrentPosition.mockImplementationOnce(
+        successHandler({ coords: mockCoordinates })
+      );
+
+      const { result } = renderHook(() => useGeolocation({}, mockCallback, false));
+
+      expect(result.current).toStrictEqual({
+        latitude: null,
+        longitude: null,
+        altitude: null,
+        accuracy: null,
+        altitudeAccuracy: null,
+        heading: null,
+        speed: null,
+        timestamp: null,
+        error: null,
+      });
+
+      requestAnimationFrame(() => {
+        expect(mockCallback).notToHaveBeenCalled();
+      });
     });
 
     it("reads initial geolocation", () => {