比如原生html         Title     function start() {         let canvas = document.querySelector('.canvas');         let ctx = canvas.getContext('2d');         canvas.width = 500; // 设置宽度         canvas.height = 900; // 设置高度     }     start() 可以设置画布的宽高，小程序里面怎么用js 控制呢？   <!-- canvas.wxml -->   <canvas type="2d" id="myCanvas"></canvas> // canvas.js Page({   onReady() {     const query = wx.createSelectorQuery()     query.select('#myCanvas')       .fields({ node: true, size: true })       .exec((res) => {         const canvas = res[0].node          canvas.width = res[0].width * dpr         canvas.height = res[0].height * dpr       })   } }) z 这样设置了没用呀 async drawCanvas(){     // 取 canvas 节点     // 此处使用 await     let canvasNode = await new Promise((resolve, reject)=>{       // 注意：若canvas是定义在在组件内，需改用       // const query = wx.createSelectorQuery().in(this)       const query = wx.createSelectorQuery()       query.select('#canvas')         .fields({ node: true, size: true })         .exec(res=>{           resolve(res[0])         })     })     let canvas = canvasNode.node,     ctx = canvas.getContext('2d')     this.canvas = canvas     this.ctx = ctx         canvas.width = width     canvas.height = height } 在外面拿到节点设置还是不行呀

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