按递增顺序添加新的输入字段

我有麻烦让我的javascript添加一个变量getElementById。我所做的是允许用户每篇文章有10个作者。该脚本显示的作者已经进入系统，现在我试图让他们添加更多的输入字段，只有点，10个字段显示。下面是我到目前为止的代码:

$y=1;
//GET EXISTING AUTHORS FOR POST
while ($getauthorsrow=$getauthorssql->fetch()) {
    $showauthor = $getauthorsrow['author'];
    $authorid = $getauthorsrow['ID'];
    echo "<input type='text' value='$showauthor' name='authorname[]'>
    <input type='hidden' value='$authorid' name='authorid[]'><br><br>";
    $y++;
}
$newy=$y-1;
?>
//SCRIPT TO ADD NEW FIELD ONLY TO THE POINT OF 10
<script language="javascript">
fields = <?php echo $newy; ?>;
    function addInput<?php echo $i; ?>() {
    if (fields != 10) {
        //HERE I'M TELLING IT TO GET text + $i (which is post number) + fields variable
        //So if it's the first post and the new field divs start a 5
        //Then it should getElementByid('text05') and continue on.
        document.getElementById('text<?php echo $i; ?>' + fields).innerHTML += "<center><input type='text' name='newauthorname[]'></center><br /><br />";
        fields += 1;
    } else {
        document.getElementById('text<?php echo $i; ?>' + fields).innerHTML += "<br />Only 10 authors allowed.";
        document.ajaxform<?php echo $i; ?>.add<?php echo $i; ?>.disabled=true;
    }
}
</script>
//HERE I'M ADDING THE NEW DIVS FOR TEXT FIELDS AND STARTING
//THEM AT WHATEVER NUMBER POST $i IT IS AND WHATEVER THE $w is.
//SO IN THE EXAMPLE IN THE JAVASCRIPT IT'D SAY id='text05'
//THIS WORKS JUST FINE
<?php
$w=$newy;
while ($w<=10) {
    echo "<div id='text".$i.$w."'></div>";
    $w++;;
}
//ECHO THE ADD AUTHOR BUTTON
echo "
<input type='button' onclick='addInput$i()' name='add$i' value='Add Author'><br>
<input type='hidden' name='count' value='$newy'>
<input type='hidden' name='id' value='$fileid'>
<input type='submit'>
</form>
";
?>

$i是从0开始的帖子号。使div工作良好的php。我只是得到null的getElementById在javascript中。我说错了什么?

<form id="ajaxform0">
    <input type="text" value="Logan" name="authorname[]">
        <input type="hidden" value="121" name="authorid[]"><br><br><input type="text" value="Matt" name="authorname[]">
        <input type="hidden" value="122" name="authorid[]"><br><br><input type="text" value="Chad" name="authorname[]">
        <input type="hidden" value="123" name="authorid[]"><br><br><input type="text" value="hey" name="authorname[]">
        <input type="hidden" value="128" name="authorid[]"><br><br><input type="text" value="jordan" name="authorname[]">
        <input type="hidden" value="129" name="authorid[]"><br><br>    
    <script language="javascript">
    fields = 5;
        function addInput0() {
        if (fields != 10) {
            var currentText = 'text0' + fields;
            document.getElementById(currentText).innerHTML += "<center><input type='text' name='newauthorname[]'></center><br /><br />";
            fields += 1;
        } else {
            document.getElementById(currentText).innerHTML += "<br />Only 10 authors allowed.";
            document.ajaxform0.add0.disabled=true;
        }
    }
    </script>
    <div id="text05"></div><div id="text06"></div><div id="text07"></div><div id="text08"></div><div id="text09"></div><div id="text010"></div>
    <input type="button" onclick="addInput0()" name="add0" value="Add Author"><br>
    <input type="hidden" name="count" value="5">
    <input type="hidden" name="id" value="45">
    <input type="submit">
    </form>