微信小程式非同步處理我使用的是promise處理，這樣能夠讓小程式執行起來邏輯更加清晰明瞭，示例程式碼如下：

let promise1 = new Promise(function (resolve, reject) {
      wx.getImageInfo({
        src: 'https://www.qiaolibeilang.com//public/uploads/images/20180809/free.png',
        success: function (res) {
          resolve(res);
        }
      })
    });

    let promise2 = new Promise(function (resolve, reject) {
      var uid = wx.getStorageSync('uid')
      console.log(uid)
      wx.getImageInfo({
        src: that.data.src1 + uid + that.data.src3,
        success: function (res) {
          resolve(res);
        }
      })
    });

    Promise.all([
      promise1, promise2
    ]).then(res => {
      var that = this
      var winWidth = wx.getSystemInfoSync().windowWidth;// 獲取當前裝置的可視寬度
      var winHeight = wx.getSystemInfoSync().windowHeight;// 獲取當前裝置的可視高度
      that.setData({
        winWidth: winWidth,
        winHeight: winHeight
      })
      console.log(winWidth)
      console.log(winHeight)
      const ctx = wx.createCanvasContext('post')
      ctx.setFillStyle('red')
      ctx.drawImage(res[0].path, 0, 0, that.data.winWidth, that.data.winWidth * 1.778)
      ctx.drawImage(res[1].path, that.data.winWidth - 160, that.data.winWidth * 1.778 - 105, 80, 80)
      console.log(res)
      ctx.draw(true)
    })
  },
 

這是我做的一個海報，上面的圖片地址是錯誤的，具體你們需要執行什麼功能就看你們自己寫了，還可以有promise3、promise4等等