onReady() {
const query = wx.createSelectorQuery()
query.select('#bar')
.fields({ node: true, size: true })
.exec((res) => {
const canvas = res[0].node
const ctx = canvas.getContext('2d')
const dpr = wx.getSystemInfoSync().pixelRatio
canvas.width = res[0].width * dpr
canvas.height = res[0].height * dpr
ctx.scale(dpr, dpr)
this.drawBarEchart(ctx,res[0].width, res[0].height)
})
