//需要同步执行的代码 
 tbcode: function(a, b, c) {
    let that = this; 
    let dm  = new Promise(function(resolve, reject) {
      wx.getImageInfo({
        src: image,
        success: function(imageInfo) { 
          resolve('success');
        }
      });
    });
    return dm;
  }
//调用
that.tbcode(a, b, c).then(isSuccess => {
          if (isSuccess == 'success') {
            //处理其他逻辑，这里保证 tbcode执行后才执行这里的代码
          }
        });

参考：https://www.jianshu.com/p/21b12589172f