1、背景

在一些可视化平台，或者canvas、svg元素用到的地方。业务都可能会提出这样的需求，当前所展示的东西我想导出图片进行查阅；

2、svg转png图片并下载

exportImg() {
      let that = this
      let serializer = new XMLSerializer()
      let svg = document.getElementById('svg')
      let toExport = svg.cloneNode(true) // 设置为 true，克隆节点及其属性，以及后代
      let bb = svg.getBBox() // 
      toExport.setAttribute('viewBox', bb.x + ' ' + bb.y + ' ' + bb.width + ' ' + bb.height) // 所有svg充满画布
      toExport.setAttribute('width', bb.width)
      toExport.setAttribute('height', bb.height)
      let source = `<?xml version="1.0" standalone="no"?>\r\n` + serializer.serializeToString(toExport)
      let image = new Image
      image.src = 'data:image/svg+xml;charset=utf-8,' + encodeURIComponent(source)
      let canvas= document.createElement('canvas')
      canvas.width = bb.width + 40
      canvas.height = bb.height + 40
      let context = canvas.getContext('2d')
      context.fillStyle = '#fff'
      context.fillRect(0, 0, 10000, 10000)
      image.onload = function() {
        context.drawImage(image, 20, 20) // canvas画图片，image base64数据
        let a = document.createElement('a')
        a.download = `${that.name}.png`
        a.href = canvas.toDataURL('image/png')
        a.click()
      }
    }
  }