[避坑]

1 组件中引用canvas【一点要加this】

let ctx = wx.createCanvasContext('posterCanvas',this); //需要加this

2 如在组件外调用组件内的canvas需要绑定上下文

drawImg(tempFilePaths, canvasWidth, canvasHeight){
    let that = this
    let cavsid = this.cavid
    let ctx = wx.createCanvasContext(cavsid, that);
    ctx.drawImage(tempFilePaths, 0, 0, canvasWidth, canvasHeight)
    ctx.draw()
    
        wx.canvasToTempFilePath({
          canvasId: cavsid,
          success: function (res) {
              ....
          }
        }, that)//就是这个that

}