JS如何账号为空保持在原页面

JS账号为空，弹窗提示后会直接跳转到登陆成功才会显示的页面，如何才能弹窗账号密码为空并保持在原页面。
<script type="text/javascript">
            
            y1.onblur=function(){
                        if(y1.value.length==0){        
                alert('账号不能为空')
                    
                    } else if(y1.value=='admin'){
                                            
                    }
                }
            y2.onblur=function(){
                        if(y2.value.length==0){                        
                alert('密码是不能为空')
                    
                    } else if(y2.value=='admin'){
                        
                    }
                }
            y3.onfocus=function(){
                if(y1.value=='admin'&&y2.value=='admin'){
                    alert('登陆成功')
                }else if(y1.value!=y2.value){
                    alert('登陆失败')  
                }
               
             window.location.href='http://127.0.0.1:8020/JS%E6%9C%9F%E6%9C%AB%E4%BD%9C%E4%B8%9A/movie.html?__hbt=1606996680410'
            }
        </script>