如何使用JavaScript更改select标签的值？

Question

I have two pages . "page1.php" "page2.php"

In page1.php ,

<a href="page2.php?c=Category1">Category1</a>
<a href="page2.php?c=Category2">Category2</a>
<a href="page2.php?c=Category3">Category3</a>

In page2.php,

<?php
    $c=$_GET['c'];
    echo '<script>'
    , 'chgvalues("'.$c.'");'
    , '</script>';
?>
<select id="mySelect">
    <option>Category1</option>
    <option>Category3</option>
    <option>Category2</option>
</select>

In chgvalues(c),

function chgvalues(c)
{
    document.getElementById("mySelect").selected =true;
}

But this ain't working for me. What I want to do is , when a user clicks on a link on page 1 then the page 2 has the select value automatically set .

I think I am wrong in this chgvalues function.

Answer 1

Change page2.php to:

<select id="mySelect">
<option id="Category1">Category1</option>
<option id="Category3">Category3</option>
<option id="Category2">Category2</option>
</select>
<?php
$c=$_GET['c'];
echo '<script>'
, 'chgvalues("'.$c.'");'
, '</script>';
?>

Your script is running before the options are in the DOM, and there are no IDs on the options so they don't match getElementById.