1、获取url中参数code； 根据code 获取openId；调用后台接口获取openId 。 参考文档：https://mp.weixin.qq.com/wiki?t=resource/res_main&id=mp1421140842

 function getUrlKey(name){//获取url 参数
   return decodeURIComponent((new RegExp('[?|&]'+name+'='+'([^&;]+?)(&|#|;|$)').exec(location.href)||[,""])[1].replace(/\+/g,'%20'))||null;
 }
  
function getCodeApi(state){//获取code   
     let urlNow=encodeURIComponent(window.location.href);
     let scope='snsapi_base';    //snsapi_userinfo   //静默授权 用户无感知
     let appid='wx4cc5d5c123123123';
     let url=`https://open.weixin.qq.com/connect/oauth2/authorize?appid=${appid}&redirect_uri=${urlNow}&response_type=code&scope=${scope}&state=${state}#wechat_redirect`;
     window.location.replace(url);
}

//注意代码放置位置
export default {
	created(){
		let code=getUrlKey("code");//获取url参数code
		if(code){ //拿到code， code传递给后台接口换取opend
			getOpenIdApi(code).then(res=>{
                 console.log(res);
            }).catch(res=>{})
		 }else{
			getCodeApi("123");
		 }
	}
}