return a resolving promise, if camera is already running

qr-scanner.min.js

@@ -1,7 +1,7 @@
 'use strict';export default class QrScanner{constructor(video,onDecode,canvasSize=QrScanner.DEFAULT_CANVAS_SIZE){this.$video=video;this.$canvas=document.createElement("canvas");this._onDecode=onDecode;this._active=false;this.$canvas.width=canvasSize;this.$canvas.height=canvasSize;this._sourceRect={x:0,y:0,width:canvasSize,height:canvasSize};this.$video.addEventListener("canplay",()=>this._updateSourceRect());this.$video.addEventListener("play",()=>{this._updateSourceRect();this._scanFrame()},false);
 this._qrWorker=new Worker(QrScanner.WORKER_PATH)}_updateSourceRect(){const smallestDimension=Math.min(this.$video.videoWidth,this.$video.videoHeight);const sourceRectSize=Math.round(2/3*smallestDimension);this._sourceRect.width=this._sourceRect.height=sourceRectSize;this._sourceRect.x=(this.$video.videoWidth-sourceRectSize)/2;this._sourceRect.y=(this.$video.videoHeight-sourceRectSize)/2}_scanFrame(){if(this.$video.paused||this.$video.ended)return false;requestAnimationFrame(()=>{QrScanner.scanImage(this.$video,
 this._sourceRect,this._qrWorker,this.$canvas,true).then(this._onDecode,(error)=>{if(error!=="QR code not found.")console.error(error)}).then(()=>this._scanFrame())})}_getCameraStream(facingMode,exact=false){const constraintsToTry=[{width:{min:1024}},{width:{min:768}},{}];if(facingMode){if(exact)facingMode={exact:facingMode};constraintsToTry.forEach((constraint)=>constraint.facingMode=facingMode)}return this._getMatchingCameraStream(constraintsToTry)}_getMatchingCameraStream(constraintsToTry){if(constraintsToTry.length===
-0)return Promise.reject("Camera not found.");return navigator.mediaDevices.getUserMedia({video:constraintsToTry.shift()}).catch(()=>this._getMatchingCameraStream(constraintsToTry))}start(){if(this._active)return;this._active=true;clearTimeout(this._offTimeout);let facingMode="environment";return this._getCameraStream("environment",true).catch(()=>{facingMode="user";return this._getCameraStream()}).then((stream)=>{this.$video.srcObject=stream;this._setVideoMirror(facingMode)})}stop(){if(!this._active)return;
+0)return Promise.reject("Camera not found.");return navigator.mediaDevices.getUserMedia({video:constraintsToTry.shift()}).catch(()=>this._getMatchingCameraStream(constraintsToTry))}start(){if(this._active)return Promise.resolve();this._active=true;clearTimeout(this._offTimeout);let facingMode="environment";return this._getCameraStream("environment",true).catch(()=>{facingMode="user";return this._getCameraStream()}).then((stream)=>{this.$video.srcObject=stream;this._setVideoMirror(facingMode)})}stop(){if(!this._active)return;
 this._active=false;this.$video.pause();this._offTimeout=setTimeout(()=>{this.$video.srcObject.getTracks()[0].stop();this.$video.srcObject=null},3E3)}_setVideoMirror(facingMode){const scaleFactor=facingMode==="user"?-1:1;this.$video.style.transform="scaleX("+scaleFactor+")"}setGrayscaleWeights(red,green,blue){this._qrWorker.postMessage({type:"grayscaleWeights",data:{red,green,blue}})}static scanImage(imageOrFileOrUrl,sourceRect=null,worker=null,canvas=null,fixedCanvasSize=false,alsoTryWithoutSourceRect=
 false){const promise=new Promise((resolve,reject)=>{worker=worker||new Worker(QrScanner.WORKER_PATH);let timeout,onMessage,onError;onMessage=(event)=>{if(event.data.type!=="qrResult")return;worker.removeEventListener("message",onMessage);worker.removeEventListener("error",onError);clearTimeout(timeout);if(event.data.data!==null)resolve(event.data.data);else reject("QR code not found.")};onError=()=>{worker.removeEventListener("message",onMessage);worker.removeEventListener("error",onError);clearTimeout(timeout);
 reject("Worker error.")};worker.addEventListener("message",onMessage);worker.addEventListener("error",onError);timeout=setTimeout(onError,3E3);QrScanner._loadImage(imageOrFileOrUrl).then((image)=>{const imageData=QrScanner._getImageData(image,sourceRect,canvas,fixedCanvasSize);worker.postMessage({type:"decode",data:imageData},[imageData.data.buffer])}).catch(reject)});if(sourceRect&&alsoTryWithoutSourceRect)return promise.catch(()=>QrScanner.scanImage(imageOrFileOrUrl,null,worker,canvas,fixedCanvasSize));

src/qr-scanner.js

@@ -70,7 +70,7 @@ export default class QrScanner {
 
     start() {
         if (this._active) {
-            return;
+            return Promise.resolve();
         }
         this._active = true;
         clearTimeout(this._offTimeout);