javascript使用H5新版媒体接口navigator.mediaDevices.getUserMedia，做扫描二维码，并识别内容

本文代码测试要求，最新的chrome浏览器(手机APP)，并且要允许chrome拍照录像权限，必须要HTTPS协议，http不支持。

原理：调用摄像头，将摄像头返回的媒体流渲染到视频标签中，再通过canvas绘制到画布上面，最后通过canvas分析二维码

兼容性只在手机中的chrome中测试通过，微信里面也能使用，但是canvas绘图很卡

测试连接

引用了第三方的qrcode.js解码，但是这个文件并未在GitHub中找到，不知道出处。源码：

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d=i-(h-i);if(d<0){e=i/(i-d);d=0}else{if(d>=qrcode.width){e=(qrcode.width-1-i)/(d-i);d=qrcode.width-1}}var c=Math.floor(g-(f-g)*e);e=1;if(c<0){e=g/(g-c);c=0}else{if(c>=qrcode.height){e=(qrcode.height-1-g)/(c-g);c=qrcode.height-1}}d=Math.floor(i+(d-i)*e);b+=this._bi(i,g,d,c);return b-1};this._bj=function(c,d){var b=this._bh(Math.floor(c.X),Math.floor(c.Y),Math.floor(d.X),Math.floor(d.Y));var e=this._bh(Math.floor(d.X),Math.floor(d.Y),Math.floor(c.X),Math.floor(c.Y));if(isNaN(b)){return e/7}if(isNaN(e)){return b/7}return(b+e)/14};this._bk=function(d,c,b){return(this._bj(d,c)+this._bj(d,b))/2};this.distance=function(c,b){xDiff=c.X-b.X;yDiff=c.Y-b.Y;return Math.sqrt((xDiff*xDiff+yDiff*yDiff))};this._bx=function(g,f,d,e){var b=Math.round(this.distance(g,f)/e);var c=Math.round(this.distance(g,d)/e);var h=((b+c)>>1)+7;switch(h&3){case 0:h++;break;case 2:h--;break;case 3:throw"Error"}return h};this._bl=function(g,f,d,j){var k=Math.floor(j*g);var h=Math.max(0,f-k);var i=Math.min(qrcode.width-1,f+k);if(i-h<g*3){throw"Error"}var b=Math.max(0,d-k);var c=Math.min(qrcode.height-1,d+k);var e=new _ak(this.image,h,b,i-h,c-b,g,this._am);return e.find()};this.createTransform=function(l,h,k,b,g){var j=g-3.5;var i;var f;var e;var c;if(b!=null){i=b.X;f=b.Y;e=c=j-3}else{i=(h.X-l.X)+k.X;f=(h.Y-l.Y)+k.Y;e=c=j}var d=_ae._ag(3.5,3.5,j,3.5,e,c,3.5,j,l.X,l.Y,h.X,h.Y,i,f,k.X,k.Y);return d};this._bz=function(e,b,d){var c=_aa;return c._af(e,d,b)};this._cd=function(r){var j=r._gq;var h=r._gs;var n=r._gp;var d=this._bk(j,h,n);if(d<1){throw"Error"}var s=this._bx(j,h,n,d);var b=_a3._at(s);var k=b._cr-7;var l=null;if(b._as.length>0){var f=h.X-j.X+n.X;var e=h.Y-j.Y+n.Y;var c=1-3/k;var u=Math.floor(j.X+c*(f-j.X));var t=Math.floor(j.Y+c*(e-j.Y));for(var q=4;q<=16;q<<=1){l=this._bl(d,u,t,q);break}}var g=this.createTransform(j,h,n,l,s);var m=this._bz(this.image,g,s);var o;if(l==null){o=new Array(n,j,h)}else{o=new Array(n,j,h,l)}return new _bg(m,o)};this.detect=function(){var b=new _cc()._ce(this.image);return this._cd(b)}}var _ca=21522;var _cb=new Array(new Array(21522,0),new Array(20773,1),new Array(24188,2),new Array(23371,3),new Array(17913,4),new Array(16590,5),new Array(20375,6),new Array(19104,7),new Array(30660,8),new Array(29427,9),new Array(32170,10),new Array(30877,11),new Array(26159,12),new Array(25368,13),new Array(27713,14),new Array(26998,15),new Array(5769,16),new Array(5054,17),new Array(7399,18),new Array(6608,19),new Array(1890,20),new Array(597,21),new Array(3340,22),new Array(2107,23),new Array(13663,24),new Array(12392,25),new Array(16177,26),new Array(14854,27),new Array(9396,28),new Array(8579,29),new Array(11994,30),new Array(11245,31));var _ch=new Array(0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4);function _ax(a){this._cf=_cg.forBits((a>>3)&3);this._fe=(a&7);this.__defineGetter__("_cg",function(){return this._cf});this.__defineGetter__("_dx",function(){return this._fe});this.GetHashCode=function(){return(this._cf.ordinal()<<3)|_fe};this.Equals=function(c){var b=c;return this._cf==b._cf&&this._fe==b._fe}}_ax._gj=function(d,c){d^=c;return _ch[d&15]+_ch[(_ew(d,4)&15)]+_ch[(_ew(d,8)&15)]+_ch[(_ew(d,12)&15)]+_ch[(_ew(d,16)&15)]+_ch[(_ew(d,20)&15)]+_ch[(_ew(d,24)&15)]+_ch[(_ew(d,28)&15)]};_ax._ci=function(a){var b=_ax._cj(a);if(b!=null){return b}return _ax._cj(a^_ca)};_ax._cj=function(d){var b=4294967295;var a=0;for(var c=0;c<_cb.length;c++){var g=_cb[c];var f=g[0];if(f==d){return new _ax(g[1])}var e=this._gj(d,f);if(e<b){a=g[1];b=e}}if(b<=3){return new _ax(a)}return null};function _cg(a,c,b){this._ff=a;this.bits=c;this.name=b;this.__defineGetter__("Bits",function(){return this.bits});this.__defineGetter__("Name",function(){return this.name});this.ordinal=function(){return this._ff}}_cg.forBits=function(a){if(a<0||a>=FOR_BITS.length){throw"bad arguments"}return FOR_BITS[a]};var L=new _cg(0,1,"L");var M=new _cg(1,0,"M");var Q=new _cg(2,3,"Q");var H=new _cg(3,2,"H");var FOR_BITS=new Array(M,L,H,Q);function _ac(d,a){if(!a){a=d}if(d<1||a<1){throw"Both dimensions must be greater than 0"}this.width=d;this.height=a;var c=d>>5;if((d&31)!=0){c++}this.rowSize=c;this.bits=new Array(c*a);for(var b=0;b<this.bits.length;b++){this.bits[b]=0}this.__defineGetter__("Width",function(){return this.width});this.__defineGetter__("Height",function(){return this.height});this.__defineGetter__("Dimension",function(){if(this.width!=this.height){throw"Can't call getDimension() on a non-square matrix"}return this.width});this._ds=function(e,g){var f=g*this.rowSize+(e>>5);return((_ew(this.bits[f],(e&31)))&1)!=0};this._dq=function(e,g){var f=g*this.rowSize+(e>>5);this.bits[f]|=1<<(e&31)};this.flip=function(e,g){var f=g*this.rowSize+(e>>5);this.bits[f]^=1<<(e&31)};this.clear=function(){var e=this.bits.length;for(var f=0;f<e;f++){this.bits[f]=0}};this._bq=function(g,j,f,m){if(j<0||g<0){throw"Left and top must be nonnegative"}if(m<1||f<1){throw"Height and width must be at least 1"}var l=g+f;var e=j+m;if(e>this.height||l>this.width){throw"The region must fit inside the matrix"}for(var i=j;i<e;i++){var h=i*this.rowSize;for(var k=g;k<l;k++){this.bits[h+(k>>5)]|=1<<(k&31)}}}}function _dl(a,b){this._dv=a;this._dw=b;this.__defineGetter__("_du",function(){return this._dv});this.__defineGetter__("Codewords",function(){return this._dw})}_dl._gn=function(c,h,s){if(c.length!=h._dp){throw"bad arguments"}var k=h._bu(s);var e=0;var d=k._fb();for(var r=0;r<d.length;r++){e+=d[r].Count}var l=new Array(e);var n=0;for(var o=0;o<d.length;o++){var f=d[o];for(var r=0;r<f.Count;r++){var m=f._dm;var t=k._bo+m;l[n++]=new _dl(m,new Array(t))}}var u=l[0]._dw.length;var b=l.length-1;while(b>=0){var w=l[b]._dw.length;if(w==u){break}b--}b++;var g=u-k._bo;var a=0;for(var r=0;r<g;r++){for(var o=0;o<n;o++){l[o]._dw[r]=c[a++]}}for(var o=b;o<n;o++){l[o]._dw[g]=c[a++]}var q=l[0]._dw.length;for(var r=g;r<q;r++){for(var o=0;o<n;o++){var v=o<b?r:r+1;l[o]._dw[v]=c[a++]}}return l};function _cl(a){var b=a.Dimension;if(b<21||(b&3)!=1){throw"Error _cl"}this._au=a;this._cp=null;this._co=null;this._dk=function(d,c,e){return this._au._ds(d,c)?(e<<1)|1:e<<1};this._cm=function(){if(this._co!=null){return this._co}var g=0;for(var e=0;e<6;e++){g=this._dk(e,8,g)}g=this._dk(7,8,g);g=this._dk(8,8,g);g=this._dk(8,7,g);for(var c=5;c>=0;c--){g=this._dk(8,c,g)}this._co=_ax._ci(g);if(this._co!=null){return this._co}var f=this._au.Dimension;g=0;var d=f-8;for(var e=f-1;e>=d;e--){g=this._dk(e,8,g)}for(var c=f-7;c<f;c++){g=this._dk(8,c,g)}this._co=_ax._ci(g);if(this._co!=null){return this._co}throw"Error _cm"};this._cq=function(){if(this._cp!=null){return this._cp}var h=this._au.Dimension;var f=(h-17)>>2;if(f<=6){return _a3._av(f)}var g=0;var e=h-11;for(var c=5;c>=0;c--){for(var d=h-9;d>=e;d--){g=this._dk(d,c,g)}}this._cp=_a3._aw(g);if(this._cp!=null&&this._cp._cr==h){return this._cp}g=0;for(var d=5;d>=0;d--){for(var c=h-9;c>=e;c--){g=this._dk(d,c,g)}}this._cp=_a3._aw(g);if(this._cp!=null&&this._cp._cr==h){return this._cp}throw"Error _cq"};this._gk=function(){var r=this._cm();var o=this._cq();var c=_dx._gl(r._dx);var f=this._au.Dimension;c._dj(this._au,f);var k=o._aq();var n=true;var s=new Array(o._dp);var m=0;var q=0;var h=0;for(var e=f-1;e>0;e-=2){if(e==6){e--}for(var l=0;l<f;l++){var g=n?f-1-l:l;for(var d=0;d<2;d++){if(!k._ds(e-d,g)){h++;q<<=1;if(this._au._ds(e-d,g)){q|=1}if(h==8){s[m++]=q;h=0;q=0}}}}n^=true}if(m!=o._dp){throw"Error _gk"}return s}}_dx={};_dx._gl=function(a){if(a<0||a>7){throw"bad arguments"}return _dx._dy[a]};function _fg(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return((b+a)&1)==0}}function _fh(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return(b&1)==0}}function _fi(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return a%3==0}}function _fj(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return(b+a)%3==0}}function _fk(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return(((_ew(b,1))+(a/3))&1)==0}}function _fl(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(c,b){var a=c*b;return(a&1)+(a%3)==0}}function _fm(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(c,b){var a=c*b;return(((a&1)+(a%3))&1)==0}}function _fn(){this._dj=function(c,d){for(var b=0;b<d;b++){for(var a=0;a<d;a++){if(this._fw(b,a)){c.flip(a,b)}}}};this._fw=function(b,a){return((((b+a)&1)+((b*a)%3))&1)==0}}_dx._dy=new Array(new _fg(),new _fh(),new _fi(),new _fj(),new _fk(),new _fl(),new _fm(),new _fn());function _db(_fa){this._fa=_fa;this.decode=function(received,_fv){var poly=new _bp(this._fa,received);var _dh=new Array(_fv);for(var i=0;i<_dh.length;i++){_dh[i]=0}var _fq=false;var noError=true;for(var i=0;i<_fv;i++){var eval=poly.evaluateAt(this._fa.exp(_fq?i+1:i));_dh[_dh.length-1-i]=eval;if(eval!=0){noError=false}}if(noError){return}var _fu=new _bp(this._fa,_dh);var _dg=this._eb(this._fa._ba(_fv,1),_fu,_fv);var sigma=_dg[0];var omega=_dg[1];var _dz=this._ey(sigma);var _ea=this._di(omega,_dz,_fq);for(var i=0;i<_dz.length;i++){var position=received.length-1-this._fa.log(_dz[i]);if(position<0){throw"ReedSolomonException Bad error location"}received[position]=_az._bd(received[position],_ea[i])}};this._eb=function(a,b,R){if(a._ec<b._ec){var temp=a;a=b;b=temp}var rLast=a;var r=b;var sLast=this._fa.One;var s=this._fa.Zero;var tLast=this._fa.Zero;var t=this._fa.One;while(r._ec>=Math.floor(R/2)){var rLastLast=rLast;var _ga=sLast;var _gb=tLast;rLast=r;sLast=s;tLast=t;if(rLast.Zero){throw"r_{i-1} was zero"}r=rLastLast;var q=this._fa.Zero;var _df=rLast._ex(rLast._ec);var _fy=this._fa.inverse(_df);while(r._ec>=rLast._ec&&!r.Zero){var _fx=r._ec-rLast._ec;var scale=this._fa.multiply(r._ex(r._ec),_fy);q=q._bd(this._fa._ba(_fx,scale));r=r._bd(rLast._dc(_fx,scale))}s=q.multiply1(sLast)._bd(_ga);t=q.multiply1(tLast)._bd(_gb)}var _de=t._ex(0);if(_de==0){throw"ReedSolomonException sigmaTilde(0) was zero"}var inverse=this._fa.inverse(_de);var sigma=t.multiply2(inverse);var omega=r.multiply2(inverse);return new Array(sigma,omega)};this._ey=function(_ez){var _fz=_ez._ec;if(_fz==1){return new Array(_ez._ex(1))}var result=new Array(_fz);var e=0;for(var i=1;i<256&&e<_fz;i++){if(_ez.evaluateAt(i)==0){result[e]=this._fa.inverse(i);e++}}if(e!=_fz){throw"Error locator degree does not match number of roots"}return result};this._di=function(_fs,_dz,_fq){var s=_dz.length;var result=new Array(s);for(var i=0;i<s;i++){var _gc=this._fa.inverse(_dz[i]);var _dr=1;for(var j=0;j<s;j++){if(i!=j){_dr=this._fa.multiply(_dr,_az._bd(1,this._fa.multiply(_dz[j],_gc)))}}result[i]=this._fa.multiply(_fs.evaluateAt(_gc),this._fa.inverse(_dr));if(_fq){result[i]=this._fa.multiply(result[i],_gc)}}return result}}function _bp(f,e){if(e==null||e.length==0){throw"bad arguments"}this._fa=f;var c=e.length;if(c>1&&e[0]==0){var d=1;while(d<c&&e[d]==0){d++}if(d==c){this._dd=f.Zero._dd}else{this._dd=new Array(c-d);for(var b=0;b<this._dd.length;b++){this._dd[b]=0}for(var a=0;a<this._dd.length;a++){this._dd[a]=e[d+a]}}}else{this._dd=e}this.__defineGetter__("Zero",function(){return this._dd[0]==0});this.__defineGetter__("_ec",function(){return this._dd.length-1});this.__defineGetter__("Coefficients",function(){return this._dd});this._ex=function(g){return this._dd[this._dd.length-1-g]};this.evaluateAt=function(h){if(h==0){return this._ex(0)}var l=this._dd.length;if(h==1){var g=0;for(var k=0;k<l;k++){g=_az._bd(g,this._dd[k])}return g}var j=this._dd[0];for(var k=1;k<l;k++){j=_az._bd(this._fa.multiply(h,j),this._dd[k])}return j};this._bd=function(g){if(this._fa!=g._fa){throw"GF256Polys do not have same _az _fa"}if(this.Zero){return g}if(g.Zero){return this}var o=this._dd;var n=g._dd;if(o.length>n.length){var j=o;o=n;n=j}var h=new Array(n.length);var k=n.length-o.length;for(var m=0;m<k;m++){h[m]=n[m]}for(var l=k;l<n.length;l++){h[l]=_az._bd(o[l-k],n[l])}return new _bp(f,h)};this.multiply1=function(o){if(this._fa!=o._fa){throw"GF256Polys do not have same _az _fa"}if(this.Zero||o.Zero){return this._fa.Zero}var r=this._dd;var g=r.length;var l=o._dd;var n=l.length;var q=new Array(g+n-1);for(var m=0;m<g;m++){var h=r[m];for(var k=0;k<n;k++){q[m+k]=_az._bd(q[m+k],this._fa.multiply(h,l[k]))}}return new _bp(this._fa,q)};this.multiply2=function(g){if(g==0){return this._fa.Zero}if(g==1){return this}var j=this._dd.length;var k=new Array(j);for(var h=0;h<j;h++){k[h]=this._fa.multiply(this._dd[h],g)}return new _bp(this._fa,k)};this._dc=function(l,g){if(l<0){throw"bad arguments"}if(g==0){return this._fa.Zero}var j=this._dd.length;var k=new Array(j+l);for(var h=0;h<k.length;h++){k[h]=0}for(var h=0;h<j;h++){k[h]=this._fa.multiply(this._dd[h],g)}return new _bp(this._fa,k)};this.divide=function(l){if(this._fa!=l._fa){throw"GF256Polys do not have same _az _fa"}if(l.Zero){throw"Divide by 0"}var j=this._fa.Zero;var o=this;var g=l._ex(l._ec);var n=this._fa.inverse(g);while(o._ec>=l._ec&&!o.Zero){var m=o._ec-l._ec;var h=this._fa.multiply(o._ex(o._ec),n);var i=l._dc(m,h);var k=this._fa._ba(m,h);j=j._bd(k);o=o._bd(i)}return new Array(j,o)}}function _az(b){this._gh=new Array(256);this._gi=new Array(256);var a=1;for(var e=0;e<256;e++){this._gh[e]=a;a<<=1;if(a>=256){a^=b}}for(var e=0;e<255;e++){this._gi[this._gh[e]]=e}var d=new Array(1);d[0]=0;this.zero=new _bp(this,new Array(d));var c=new Array(1);c[0]=1;this.one=new _bp(this,new Array(c));this.__defineGetter__("Zero",function(){return this.zero});this.__defineGetter__("One",function(){return this.one});this._ba=function(j,f){if(j<0){throw"bad arguments"}if(f==0){return zero}var h=new Array(j+1);for(var g=0;g<h.length;g++){h[g]=0}h[0]=f;return new _bp(this,h)};this.exp=function(f){return this._gh[f]};this.log=function(f){if(f==0){throw"bad arguments"}return this._gi[f]};this.inverse=function(f){if(f==0){throw"System.ArithmeticException"}return this._gh[255-this._gi[f]]};this.multiply=function(g,f){if(g==0||f==0){return 0}if(g==1){return f}if(f==1){return g}return this._gh[(this._gi[g]+this._gi[f])%255]}}_az._bb=new _az(285);_az._bc=new _az(301);_az._bd=function(d,c){return d^c};Decoder={};Decoder.rsDecoder=new _db(_az._bb);Decoder.correctErrors=function(g,b){var d=g.length;var f=new Array(d);for(var e=0;e<d;e++){f[e]=g[e]&255}var a=g.length-b;try{Decoder.rsDecoder.decode(f,a)}catch(c){throw c}for(var e=0;e<b;e++){g[e]=f[e]}};Decoder.decode=function(r){var b=new _cl(r);var o=b._cq();var c=b._cm()._cg;var q=b._gk();var a=_dl._gn(q,o,c);var f=0;for(var k=0;k<a.length;k++){f+=a[k]._du}var e=new Array(f);var n=0;for(var h=0;h<a.length;h++){var m=a[h];var d=m.Codewords;var g=m._du;Decoder.correctErrors(d,g);for(var k=0;k<g;k++){e[n++]=d[k]}}var l=new QRCodeDataBlockReader(e,o._fd,c.Bits);return l};qrcode={};qrcode.imagedata=null;qrcode.width=0;qrcode.height=0;qrcode.qrCodeSymbol=null;qrcode.debug=false;qrcode.maxImgSize=1024*1024;qrcode._eo=[[10,9,8,8],[12,11,16,10],[14,13,16,12]];qrcode.callback=null;qrcode.decode=function(d){if(arguments.length==0){var b=document.getElementById("qr-canvas");var a=b.getContext("2d");qrcode.width=b.width;qrcode.height=b.height;qrcode.imagedata=a.getImageData(0,0,qrcode.width,qrcode.height);qrcode.result=qrcode.process(a);if(qrcode.callback!=null){qrcode.callback(qrcode.result)}return qrcode.result}else{var c=new Image();c.onload=function(){var g=document.getElementById("out-canvas");if(g!=null){var j=g.getContext("2d");j.clearRect(0,0,320,240);j.drawImage(c,0,0,320,240)}var i=document.createElement("canvas");var h=i.getContext("2d");var f=c.height;var l=c.width;if(c.width*c.height>qrcode.maxImgSize){var k=c.width/c.height;f=Math.sqrt(qrcode.maxImgSize/k);l=k*f}i.width=l;i.height=f;h.drawImage(c,0,0,i.width,i.height);qrcode.width=i.width;qrcode.height=i.height;try{qrcode.imagedata=h.getImageData(0,0,i.width,i.height)}catch(m){qrcode.result="Cross domain image reading not supported in your browser! Save it to your computer then drag and drop the file!";if(qrcode.callback!=null){qrcode.callback(qrcode.result)}return}try{qrcode.result=qrcode.process(h)}catch(m){console.log(m);qrcode.result="error decoding QR Code"}if(qrcode.callback!=null){qrcode.callback(qrcode.result)}};c.src=d}};qrcode.isUrl=function(a){var b=/(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%@!\-\/]))?/;return b.test(a)};qrcode.decode_url=function(b){var d="";try{d=escape(b)}catch(c){console.log(c);d=b}var a="";try{a=decodeURIComponent(d)}catch(c){console.log(c);a=d}return a};qrcode.decode_utf8=function(a){if(qrcode.isUrl(a)){return qrcode.decode_url(a)}else{return a}};qrcode.process=function(r){var a=new Date().getTime();var c=qrcode.grayScaleToBitmap(qrcode.grayscale());if(qrcode.debug){for(var m=0;m<qrcode.height;m++){for(var n=0;n<qrcode.width;n++){var o=(n*4)+(m*qrcode.width*4);qrcode.imagedata.data[o]=c[n+m*qrcode.width]?0:0;qrcode.imagedata.data[o+1]=c[n+m*qrcode.width]?0:0;qrcode.imagedata.data[o+2]=c[n+m*qrcode.width]?255:0}}r.putImageData(qrcode.imagedata,0,0)}var h=new Detector(c);var q=h.detect();if(qrcode.debug){r.putImageData(qrcode.imagedata,0,0)}var k=Decoder.decode(q.bits);var g=k.DataByte;var l="";for(var f=0;f<g.length;f++){for(var e=0;e<g[f].length;e++){l+=String.fromCharCode(g[f][e])}}var d=new Date().getTime();var b=d-a;console.log(b);return qrcode.decode_utf8(l)};qrcode.getPixel=function(a,b){if(qrcode.width<a){throw"point error"}if(qrcode.height<b){throw"point error"}point=(a*4)+(b*qrcode.width*4);p=(qrcode.imagedata.data[point]*33+qrcode.imagedata.data[point+1]*34+qrcode.imagedata.data[point+2]*33)/100;return p};qrcode.binarize=function(d){var c=new Array(qrcode.width*qrcode.height);for(var e=0;e<qrcode.height;e++){for(var b=0;b<qrcode.width;b++){var a=qrcode.getPixel(b,e);c[b+e*qrcode.width]=a<=d?true:false}}return c};qrcode._em=function(d){var c=4;var k=Math.floor(qrcode.width/c);var j=Math.floor(qrcode.height/c);var f=new Array(c);for(var g=0;g<c;g++){f[g]=new Array(c);for(var e=0;e<c;e++){f[g][e]=new Array(0,0)}}for(var o=0;o<c;o++){for(var a=0;a<c;a++){f[a][o][0]=255;for(var l=0;l<j;l++){for(var n=0;n<k;n++){var h=d[k*a+n+(j*o+l)*qrcode.width];if(h<f[a][o][0]){f[a][o][0]=h}if(h>f[a][o][1]){f[a][o][1]=h}}}}}var m=new Array(c);for(var b=0;b<c;b++){m[b]=new Array(c)}for(var o=0;o<c;o++){for(var a=0;a<c;a++){m[a][o]=Math.floor((f[a][o][0]+f[a][o][1])/2)}}return m};qrcode.grayScaleToBitmap=function(f){var j=qrcode._em(f);var b=j.length;var e=Math.floor(qrcode.width/b);var d=Math.floor(qrcode.height/b);var c=new Array(qrcode.height*qrcode.width);for(var i=0;i<b;i++){for(var a=0;a<b;a++){for(var g=0;g<d;g++){for(var h=0;h<e;h++){c[e*a+h+(d*i+g)*qrcode.width]=(f[e*a+h+(d*i+g)*qrcode.width]<j[a][i])?true:false}}}}return c};qrcode.grayscale=function(){var c=new Array(qrcode.width*qrcode.height);for(var d=0;d<qrcode.height;d++){for(var b=0;b<qrcode.width;b++){var a=qrcode.getPixel(b,d);c[b+d*qrcode.width]=a}}return c};function _ew(a,b){if(a>=0){return a>>b}else{return(a>>b)+(2<<~b)}}Array.prototype.remove=function(c,b){var a=this.slice((b||c)+1||this.length);this.length=c<0?this.length+c:c;return this.push.apply(this,a)};var _gf=3;var _eh=57;var _el=8;var _eg=2;qrcode._er=function(c){function b(l,k){xDiff=l.X-k.X;yDiff=l.Y-k.Y;return Math.sqrt((xDiff*xDiff+yDiff*yDiff))}function d(k,o,n){var m=o.x;var l=o.y;return((n.x-m)*(k.y-l))-((n.y-l)*(k.x-m))}var i=b(c[0],c[1]);var f=b(c[1],c[2]);var e=b(c[0],c[2]);var a,j,h;if(f>=i&&f>=e){j=c[0];a=c[1];h=c[2]}else{if(e>=f&&e>=i){j=c[1];a=c[0];h=c[2]}else{j=c[2];a=c[0];h=c[1]}}if(d(a,j,h)<0){var g=a;a=h;h=g}c[0]=a;c[1]=j;c[2]=h};function _cz(c,a,b){this.x=c;this.y=a;this.count=1;this._aj=b;this.__defineGetter__("_ei",function(){return this._aj});this.__defineGetter__("Count",function(){return this.count});this.__defineGetter__("X",function(){return this.x});this.__defineGetter__("Y",function(){return this.y});this._ek=function(){this.count++};this._ev=function(f,e,d){if(Math.abs(e-this.y)<=f&&Math.abs(d-this.x)<=f){var g=Math.abs(f-this._aj);return g<=1||g/this._aj<=1}return false}}function _es(a){this._go=a[0];this._gu=a[1];this._gr=a[2];this.__defineGetter__("_gp",function(){return this._go});this.__defineGetter__("_gq",function(){return this._gu});this.__defineGetter__("_gs",function(){return this._gr})}function _cc(){this.image=null;this._cv=[];this._ge=false;this._al=new Array(0,0,0,0,0);this._am=null;this.__defineGetter__("_da",function(){this._al[0]=0;this._al[1]=0;this._al[2]=0;this._al[3]=0;this._al[4]=0;return this._al});this._ao=function(f){var b=0;for(var d=0;d<5;d++){var e=f[d];if(e==0){return false}b+=e}if(b<7){return false}var c=Math.floor((b<<_el)/7);var a=Math.floor(c/2);return Math.abs(c-(f[0]<<_el))<a&&Math.abs(c-(f[1]<<_el))<a&&Math.abs(3*c-(f[2]<<_el))<3*a&&Math.abs(c-(f[3]<<_el))<a&&Math.abs(c-(f[4]<<_el))<a};this._an=function(b,a){return(a-b[4]-b[3])-b[2]/2};this._ap=function(a,j,d,g){var c=this.image;var h=qrcode.height;var b=this._da;var f=a;while(f>=0&&c[j+f*qrcode.width]){b[2]++;f--}if(f<0){return NaN}while(f>=0&&!c[j+f*qrcode.width]&&b[1]<=d){b[1]++;f--}if(f<0||b[1]>d){return NaN}while(f>=0&&c[j+f*qrcode.width]&&b[0]<=d){b[0]++;f--}if(b[0]>d){return NaN}f=a+1;while(f<h&&c[j+f*qrcode.width]){b[2]++;f++}if(f==h){return NaN}while(f<h&&!c[j+f*qrcode.width]&&b[3]<d){b[3]++;f++}if(f==h||b[3]>=d){return NaN}while(f<h&&c[j+f*qrcode.width]&&b[4]<d){b[4]++;f++}if(b[4]>=d){return NaN}var e=b[0]+b[1]+b[2]+b[3]+b[4];if(5*Math.abs(e-g)>=2*g){return NaN}return this._ao(b)?this._an(b,f):NaN};this._ej=function(b,a,e,h){var d=this.image;var i=qrcode.width;var c=this._da;var g=b;while(g>=0&&d[g+a*qrcode.width]){c[2]++;g--}if(g<0){return NaN}while(g>=0&&!d[g+a*qrcode.width]&&c[1]<=e){c[1]++;g--}if(g<0||c[1]>e){return NaN}while(g>=0&&d[g+a*qrcode.width]&&c[0]<=e){c[0]++;g--}if(c[0]>e){return NaN}g=b+1;while(g<i&&d[g+a*qrcode.width]){c[2]++;g++}if(g==i){return NaN}while(g<i&&!d[g+a*qrcode.width]&&c[3]<e){c[3]++;g++}if(g==i||c[3]>=e){return NaN}while(g<i&&d[g+a*qrcode.width]&&c[4]<e){c[4]++;g++}if(c[4]>=e){return NaN}var f=c[0]+c[1]+c[2]+c[3]+c[4];if(5*Math.abs(f-h)>=h){return NaN}return this._ao(c)?this._an(c,g):NaN};this._cu=function(c,f,e){var d=c[0]+c[1]+c[2]+c[3]+c[4];var n=this._an(c,e);var b=this._ap(f,Math.floor(n),c[2],d);if(!isNaN(b)){n=this._ej(Math.floor(n),Math.floor(b),c[2],d);if(!isNaN(n)){var l=d/7;var m=false;var h=this._cv.length;for(var g=0;g<h;g++){var a=this._cv[g];if(a._ev(l,b,n)){a._ek();m=true;break}}if(!m){var k=new _cz(n,b,l);this._cv.push(k);if(this._am!=null){this._am._ep(k)}}return true}}return false};this._ee=function(){var h=this._cv.length;if(h<3){throw"Couldn't find enough finder patterns"}if(h>3){var b=0;var j=0;for(var d=0;d<h;d++){var g=this._cv[d]._ei;b+=g;j+=(g*g)}var a=b/h;this._cv.sort(function(m,l){var k=Math.abs(l._ei-a);var i=Math.abs(m._ei-a);if(k<i){return(-1)}else{if(k==i){return 0}else{return 1}}});var e=Math.sqrt(j/h-a*a);var c=Math.max(0.2*a,e);for(var d=0;d<this._cv.length&&this._cv.length>3;d++){var f=this._cv[d];if(Math.abs(f._ei-a)>c){this._cv.remove(d);d--}}}if(this._cv.length>3){this._cv.sort(function(k,i){if(k.count>i.count){return -1}if(k.count<i.count){return 1}return 0})}return new Array(this._cv[0],this._cv[1],this._cv[2])};this._eq=function(){var b=this._cv.length;if(b<=1){return 0}var c=null;for(var d=0;d<b;d++){var a=this._cv[d];if(a.Count>=_eg){if(c==null){c=a}else{this._ge=true;return Math.floor((Math.abs(c.X-a.X)-Math.abs(c.Y-a.Y))/2)}}}return 0};this._cx=function(){var g=0;var c=0;var a=this._cv.length;for(var d=0;d<a;d++){var f=this._cv[d];if(f.Count>=_eg){g++;c+=f._ei}}if(g<3){return false}var e=c/a;var b=0;for(var d=0;d<a;d++){f=this._cv[d];b+=Math.abs(f._ei-e)}return b<=0.05*c};this._ce=function(e){var o=false;this.image=e;var n=qrcode.height;var k=qrcode.width;var a=Math.floor((3*n)/(4*_eh));if(a<_gf||o){a=_gf}var g=false;var d=new Array(5);for(var h=a-1;h<n&&!g;h+=a){d[0]=0;d[1]=0;d[2]=0;d[3]=0;d[4]=0;var b=0;for(var f=0;f<k;f++){if(e[f+h*qrcode.width]){if((b&1)==1){b++}d[b]++}else{if((b&1)==0){if(b==4){if(this._ao(d)){var c=this._cu(d,h,f);if(c){a=2;if(this._ge){g=this._cx()}else{var m=this._eq();if(m>d[2]){h+=m-d[2]-a;f=k-1}}}else{do{f++}while(f<k&&!e[f+h*qrcode.width]);f--}b=0;d[0]=0;d[1]=0;d[2]=0;d[3]=0;d[4]=0}else{d[0]=d[2];d[1]=d[3];d[2]=d[4];d[3]=1;d[4]=0;b=3}}else{d[++b]++}}else{d[b]++}}}if(this._ao(d)){var c=this._cu(d,h,k);if(c){a=d[0];if(this._ge){g=_cx()}}}}var l=this._ee();qrcode._er(l);return new _es(l)}}function _ai(c,a,b){this.x=c;this.y=a;this.count=1;this._aj=b;this.__defineGetter__("_ei",function(){return this._aj});this.__defineGetter__("Count",function(){return this.count});this.__defineGetter__("X",function(){return Math.floor(this.x)});this.__defineGetter__("Y",function(){return Math.floor(this.y)});this._ek=function(){this.count++};this._ev=function(f,e,d){if(Math.abs(e-this.y)<=f&&Math.abs(d-this.x)<=f){var g=Math.abs(f-this._aj);return g<=1||g/this._aj<=1}return false}}function _ak(g,c,b,f,a,e,d){this.image=g;this._cv=new Array();this.startX=c;this.startY=b;this.width=f;this.height=a;this._ef=e;this._al=new Array(0,0,0);this._am=d;this._an=function(i,h){return(h-i[2])-i[1]/2};this._ao=function(l){var k=this._ef;var h=k/2;for(var j=0;j<3;j++){if(Math.abs(k-l[j])>=h){return false}}return true};this._ap=function(h,r,l,o){var k=this.image;var q=qrcode.height;var j=this._al;j[0]=0;j[1]=0;j[2]=0;var n=h;while(n>=0&&k[r+n*qrcode.width]&&j[1]<=l){j[1]++;n--}if(n<0||j[1]>l){return NaN}while(n>=0&&!k[r+n*qrcode.width]&&j[0]<=l){j[0]++;n--}if(j[0]>l){return NaN}n=h+1;while(n<q&&k[r+n*qrcode.width]&&j[1]<=l){j[1]++;n++}if(n==q||j[1]>l){return NaN}while(n<q&&!k[r+n*qrcode.width]&&j[2]<=l){j[2]++;n++}if(j[2]>l){return NaN}var m=j[0]+j[1]+j[2];if(5*Math.abs(m-o)>=2*o){return NaN}return this._ao(j)?this._an(j,n):NaN};this._cu=function(l,o,n){var m=l[0]+l[1]+l[2];var u=this._an(l,n);var k=this._ap(o,Math.floor(u),2*l[1],m);if(!isNaN(k)){var t=(l[0]+l[1]+l[2])/3;var r=this._cv.length;for(var q=0;q<r;q++){var h=this._cv[q];if(h._ev(t,k,u)){return new _ai(u,k,t)}}var s=new _ai(u,k,t);this._cv.push(s);if(this._am!=null){this._am._ep(s)}}return null};this.find=function(){var q=this.startX;var t=this.height;var r=q+f;var s=b+(t>>1);var m=new Array(0,0,0);for(var k=0;k<t;k++){var o=s+((k&1)==0?((k+1)>>1):-((k+1)>>1));m[0]=0;m[1]=0;m[2]=0;var n=q;while(n<r&&!g[n+qrcode.width*o]){n++}var h=0;while(n<r){if(g[n+o*qrcode.width]){if(h==1){m[h]++}else{if(h==2){if(this._ao(m)){var l=this._cu(m,o,n);if(l!=null){return l}}m[0]=m[2];m[1]=1;m[2]=0;h=1}else{m[++h]++}}}else{if(h==1){h++}m[h]++}n++}if(this._ao(m)){var l=this._cu(m,o,r);if(l!=null){return l}}}if(!(this._cv.length==0)){return this._cv[0]}throw"Couldn't find enough alignment patterns"}}function QRCodeDataBlockReader(c,a,b){this._ed=0;this._cw=7;this.dataLength=0;this.blocks=c;this._en=b;if(a<=9){this.dataLengthMode=0}else{if(a>=10&&a<=26){this.dataLengthMode=1}else{if(a>=27&&a<=40){this.dataLengthMode=2}}}this._gd=function(f){var k=0;if(f<this._cw+1){var m=0;for(var e=0;e<f;e++){m+=(1<<e)}m<<=(this._cw-f+1);k=(this.blocks[this._ed]&m)>>(this._cw-f+1);this._cw-=f;return k}else{if(f<this._cw+1+8){var j=0;for(var e=0;e<this._cw+1;e++){j+=(1<<e)}k=(this.blocks[this._ed]&j)<<(f-(this._cw+1));this._ed++;k+=((this.blocks[this._ed])>>(8-(f-(this._cw+1))));this._cw=this._cw-f%8;if(this._cw<0){this._cw=8+this._cw}return k}else{if(f<this._cw+1+16){var j=0;var h=0;for(var e=0;e<this._cw+1;e++){j+=(1<<e)}var g=(this.blocks[this._ed]&j)<<(f-(this._cw+1));this._ed++;var d=this.blocks[this._ed]<<(f-(this._cw+1+8));this._ed++;for(var e=0;e<f-(this._cw+1+8);e++){h+=(1<<e)}h<<=8-(f-(this._cw+1+8));var l=(this.blocks[this._ed]&h)>>(8-(f-(this._cw+1+8)));k=g+d+l;this._cw=this._cw-(f-8)%8;if(this._cw<0){this._cw=8+this._cw}return k}else{return 0}}}};this.NextMode=function(){if((this._ed>this.blocks.length-this._en-2)){return 0}else{return this._gd(4)}};this.getDataLength=function(d){var e=0;while(true){if((d>>e)==1){break}e++}return this._gd(qrcode._eo[this.dataLengthMode][e])};this.getRomanAndFigureString=function(h){var f=h;var g=0;var j="";var d=new Array("0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"," ","$","%","*","+","-",".","/",":");do{if(f>1){g=this._gd(11);var i=Math.floor(g/45);var e=g%45;j+=d[i];j+=d[e];f-=2}else{if(f==1){g=this._gd(6);j+=d[g];f-=1}}}while(f>0);return j};this.getFigureString=function(f){var d=f;var e=0;var g="";do{if(d>=3){e=this._gd(10);if(e<100){g+="0"}if(e<10){g+="0"}d-=3}else{if(d==2){e=this._gd(7);if(e<10){g+="0"}d-=2}else{if(d==1){e=this._gd(4);d-=1}}}g+=e}while(d>0);return g};this.get8bitByteArray=function(g){var e=g;var f=0;var d=new Array();do{f=this._gd(8);d.push(f);e--}while(e>0);return d};this.getKanjiString=function(j){var g=j;var i=0;var h="";do{i=_gd(13);var e=i%192;var f=i/192;var k=(f<<8)+e;var d=0;if(k+33088<=40956){d=k+33088}else{d=k+49472}h+=String.fromCharCode(d);g--}while(g>0);return h};this.__defineGetter__("DataByte",function(){var g=new Array();var e=1;var f=2;var d=4;var n=8;do{var k=this.NextMode();if(k==0){if(g.length>0){break}else{throw"Empty data block"}}if(k!=e&&k!=f&&k!=d&&k!=n){throw"Invalid mode: "+k+" in (block:"+this._ed+" bit:"+this._cw+")"}dataLength=this.getDataLength(k);if(dataLength<1){throw"Invalid data length: "+dataLength}switch(k){case e:var l=this.getFigureString(dataLength);var i=new Array(l.length);for(var h=0;h<l.length;h++){i[h]=l.charCodeAt(h)}g.push(i);break;case f:var l=this.getRomanAndFigureString(dataLength);var i=new Array(l.length);for(var h=0;h<l.length;h++){i[h]=l.charCodeAt(h)}g.push(i);break;case d:var m=this.get8bitByteArray(dataLength);g.push(m);break;case n:var l=this.getKanjiString(dataLength);g.push(l);break}}while(true);return g})};

整个页面源码：

 <html>

 <head>
   <meta charset="UTF-8">
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta http-equiv="X-UA-Compatible" content="ie=edge">
   <title>js唤起摄像头识别二维码</title>
   <style>
     #scan {
       display: block;
     }
     #qr-canvas {
       max-width: 300px;
     }
   </style>
 </head>

 <body>
   <div><a href="/" target="_blank">本站首页</a></div>
   <hr>
   <div>兼容性只在手机中的chrome中测试通过，微信里面也能使用，但是canvas绘图很卡</div>
   <div>原理：调用摄像头，将摄像头返回的媒体流渲染到视频标签中，再通过canvas绘制到画布上面，最后通过canvas分析二维码</div>
   <hr>
   <a href="javascript:;" id="scan">扫码</a>
   <div id="output"></div>
   <!-- 由于llqrcode.js中写死了id，所以id必须为qr-canvas -->
   <canvas id="qr-canvas"></canvas>
   <video id="video" muted autoplay width="300" height="200"></video>
   <script src="https://cdn.bootcss.com/vConsole/3.2.0/vconsole.min.js"></script>
   <script>
     let vConsole = new VConsole();
   </script>
   <script type="text/javascript" src="llqrcode.js"></script>
   <script type="text/javascript">

     const Scan = {
       videoInputDevice: [],
       videoElement: document.getElementById("video"),
       canvasElement: document.getElementById("qr-canvas"),
       decodeTimer: null,
       canvasTimer: null,
       canvasContext: document.getElementById("qr-canvas").getContext("2d"),
       // 获取到的媒体设备
       gotDevices (deviceInfos) {
         let that = this;
         for (let i = 0; i !== deviceInfos.length; ++i) {
           let deviceInfo = deviceInfos[i];
           if (deviceInfo.kind === 'audioinput') {
             // 音频设备
           } else if (deviceInfo.kind === 'videoinput') {
             // 视频设备
             that.videoInputDevice.push(deviceInfo);
           } else {
             // 其他设备
             console.log('Found one other kind of source/device: ', deviceInfo);
           }
         }
       },
       getStream () {
         let that = this;
         if (window.stream) {
           window.stream.getTracks().forEach((track) => {
             track.stop();
           });
         }

         let constraints = {
           // 包含audio 可声明音频设备调用
           // 声明视频设备调用
           // video: true
           video: {
             deviceId: {
               // [1].deviceId 表示后置摄像头,默认开启的是前置摄像头
               exact: that.videoInputDevice[1].deviceId
             }
           }
         };

         /* // 微信里面此方法无效开启后置摄像头无效，必须使用 deviceId 开启
         // 在chrome浏览器中可使用此方法开启后置摄像头
         let front = false;
         let constraints = {
           video: {
             // environment表示后置摄像头
             // user表示前置摄像头
             facingMode: (front? "user" : "environment")
           }
         }; */

         // 视频设备初始化
         navigator.mediaDevices.getUserMedia(constraints).then(that.gotStream.bind(that)).catch(that.handleError.bind(that));
         that.captureToCanvas();
         that.decode();
       },

       // 解码
       decode () {
         let that = this;
         try {
           qrcode.decode();
         } catch (e) {
           console.log(e);
         };
         that.decodeTimer = setTimeout(that.decode.bind(that), 1000); // 解码频率为1秒一次
       },

       //将视频流放到画布
       captureToCanvas () {
         let that = this;
         try {
           // 根据视频大小设置canvas大小
           let w = that.videoElement.videoWidth;
           let h = that.videoElement.videoHeight;
           that.canvasElement.width = w;
           that.canvasElement.height = h;
           that.canvasContext.drawImage(that.videoElement, 0, 0, w, h);
         } catch (e) {
           console.log(e);
         };
         // 200毫秒绘制一次
         that.canvasTimer = setTimeout(that.captureToCanvas.bind(that), 200);
       },

       handleError (error) {
         console.log('Error: ', error);
       },

       gotStream (stream) {
         let that = this;
         window.stream = stream; // make stream available to console
         that.videoElement.srcObject = stream;
       },

       init () {
         let that = this;
         // API参考
         // https://developer.mozilla.org/zh-CN/docs/Web/API/MediaDevices/enumerateDevices
         // 先获取设备列表，方便调用后置摄像头
         let devices = navigator.mediaDevices.enumerateDevices().then(that.gotDevices.bind(that));
         document.querySelector('#scan').addEventListener('click', () => {
           document.getElementById('output').innerHTML = '';
           that.videoElement.style.display = 'block';
           that.canvasElement.style.display = 'block';

           devices.then(that.getStream.bind(that)).catch(that.handleError.bind(that));

           that.canvasContext.clearRect(0, 0, 300, 200);
           //结果回调
           qrcode.callback = (e) => {
             // 清除画布，停止摄像头
             clearTimeout(that.decodeTimer);
             clearTimeout(that.canvasTimer);
             that.canvasContext.clearRect(0, 0, 300, 200);
             if (window.stream) {
               window.stream.getTracks().forEach((track) => {
                 track.stop();
               });
             }
             that.videoElement.style.display = 'none';
             that.canvasElement.style.display = 'none';

             document.getElementById('output').innerHTML = '结果：' + e;
           }
         });
       }
     };
     Scan.init();
   </script>
 </body>

 </html>