In fact, jquery press enter to submit data is a very simple thing, we just need to check that the user press enter to directly bind the event. The core code  

$(document).ready(function(){
$(" Press the enter control ").keydown(function(e){
var curKey = e.which;
if(curKey == 13){
$("# Enter event button control ").click();
return false;
}
});
});
 

It is to support the carriage return event with the ajax function of js

document.onkeydown = function (e) {
var theEvent = window.event || e;
var code = theEvent.keyCode || theEvent.which;
if (code == 13) {
$("#login_submit").click();
}
} 

$(document).ready(function() {
    //Log in to submit
    $("#login_submit").bind('click',function(){
        var username=$("#username").val();
        var password=$("#password").val();

        $.ajax({
                type : 'POST',
                url : './login.php',
                data: {type :'ajax',username:username,password:password},
                success : function(msg){
                    //alert(msg);
                    if(msg==-1){
                        alert(' The username cannot be empty ');
                        $("#username").focus();
                    }
                    if(msg==-2){
                        alert(' The username does not exist ');
                        $("#username").val("");
                        $("#username").focus();
                    }
                    if(msg==-3){
                        alert(' The password cannot be empty ');
                        $("#password").focus();
                    }
                    if(msg==-6){
                        alert(' The password was not entered correctly ');
                        $("#password").focus();
                    }
                    if(msg==1){
                        //Alert (' login successful ');
                        window.location.href='./index.php';
                    }

                }
            });
    });

});