表单验证，计算javascript中字符串的最小值和最大值

Question

I am new in java script, can any body help.

This code is to validate whether the userid is available in database and works fine for me. But I also need to validate the min and max length of the string when user enter the user id.

<input type="text" id="userid" name="userid" class="form-control" data-required="true" onblur="return check_userexist();">
    <div id="InfoUsername"></div>



 function check_userexist(){

        var username = $("#userid").val();
        if(username.length > 0){
            $.post("/users/validator/check_username.php", {
                username: $('#userid').val(),
            }, function(response){
                 $('#InfoUsername').fadeOut();
                setTimeout("finishAjax('InfoUsername', '"+escape(response)+"')", 100);
            });
            return false;
        }
    }

php code :

if($_REQUEST)
{
    $user   = $_REQUEST['userid'];
    if ($users->CountUsernameExist($user) >0) {
    echo 'Not Available!';
    }else{
    echo 'Ok available';
    } ;     
}   

Answer 1

if(username.length >= MIN_LENGTH && username.length <= MAX_LENGTH){
    //allright

Here we've checking MIN and MAX length of value of username

Answer 2

Check min & max length in if condition. Exampe

if(username.length > min_val && username.length <= max_val){
    //Your codes
}else{
    //alert('Your alert message to user!');
    $('#InfoUsername').html('<span style="color: #f00;">Your alert message to user</span>');
    //or
    //$('#InfoUsername').text('Your alert message to user');
}

Answer 3

There is a pure html5 solution for this, not using javascript. You can use the pattern attribute as below, where min, max are the 2 boundary numbers:

 <input type="text" id="userid" name="userid" pattern=".{min,max}" required 
class="form-control" data-required="true" onblur="return check_userexist();">

See pattern attribute

Answer 4

Remember checking also in the php side, just in case Javascript is disable So use:

if(username.length > 0 && username.length <= ANY_VALUE) {

/* ALSO ADD THIS IN PHP */
if ( strlen($user) > 0 || strlen($user) < ANY_VALUE )