luruxi commented on issue #9383: echarts渲染不出来报错 URL: https://github.com/apache/incubator-echarts/issues/9383#issuecomment-494314107 > I have solved this problem in my project. > > When I debuged my project, it would sometimes log the errors like this: >  > > From the errors tips, it significantly show that this error appeared when execute this code: > > ``` > this.ctx.dpr = this.dpr > ``` > > in `Layer.js` 、`Painter.js`、`zrender.js` etc. > > So I detect the Layer.js file, in `node_modules\zrender\lib\Layer.js` , I saw this code in a function named 'initContext': > > ``` > initContext: function () { > this.ctx = this.dom.getContext('2d'); > this.ctx.dpr = this.dpr; > }, > ``` > > I modified this function to the code below: > > ``` > initContext: function () { > this.ctx = this.dom.getContext('2d'); > try { > this.ctx.dpr = this.dpr; > } catch (e) { > setTimeout(() => { > location.reload() > }, 500) > } > }, > ``` > > And the bug resolved. > > I think this is a iOS bug happened occasionally, when the Layer.js or other Javascript library execute the command like `this.ctx = this.dom.getContext('2d');`，the lib find `this.dom` is not found, `this.dom` here represent the HTMLCanvasElement. It exactly is a canvas element in most time, when the iOS javascript engines display correctly, but sometimes it would not, it was not found instead. So `this.ctx` is `null`, so it will throw error when execute `this.ctx.dpr = this.dpr;`. Thank you. I'll try
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