新建一个小程序项目， 1、在pages/index.wxml中加入：  <canvas type='2d' id='testcanv' style='width:100%;height:300px'></canvas> 2、在app.js：onLoad中加入：  wx.createSelectorQuery().select('#testcanv').node((res)=>{       if (res && res.node) {         let {node:canvas}=res                console.log('found node!')         wx.getSystemInfo({success:sysinfo=>{           let s = "hello world"           let ctx = canvas.getContext('2d')           ctx.font = "32px bold Arial"           let w=ctx.measureText(s).width                              ctx.fillText(s, sysinfo.screenWidth/2-w/2, 32)         }})       }       else console.log('node not found')     }).exec()  3、点击远程调试（测试机分别使用iPhoneXR 及 华为M6 pad, 系统及微信均更新到最新版), 开发工具抛出以下异常：  runtime.js?devtools_ignore=true:1 eval script evaluate_id #12 failed TypeError: r.Canvas is not a constructor     at n.value (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:733280)     at n.value (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:621289)     at t (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:621461)     at b (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:620332)     at eval (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:732657)     at eval (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:717590)     at Object.m (eval at n.call.document (runtime.js?devtools_ignore=true:1), <anonymous>:2:77498)     at Object.value [as subscribeHandler] (runtime.js?devtools_ignore=true:1)     at eval (eval at c (runtime.js?devtools_ignore=true:1), <anonymous>:1:17)     at eval (<anonymous>)