Append Text To End Of Search Entry

My work website, [URL] has an activity search on the top-right side of the page that searches congregation details. It mostly works fine, except that if you search "greenwood" instead of getting shown Greenwood Uniting Church, it tells you that there are no congregations within 15km of Greenwood. Yet if you search "Kingsley" (Next suburb over, less than 15km from Greenwood) it finds the Greenwood Uniting Church.

We worked out that the issue is that there is more than one Greenwood in Australia, so it needs to be clarified that the state of WA needs to be added to the search. The easiest way (I feel) is to check whether WA has been included in the text, and if not, to add it to the search text. This is the code I've got so far (written by a friend, who wasn't certain whether it would work or not):

PHP Code:
echo '<script type="text/javascript">';
// Check that there's state appended to the search
echo 'function checkState(){';
echo 'var searchField=document.getElementById("suburb-address");';
echo 'if (searchField.value.lastindexOf("WA")==0) { ';
echo 'searchField.value+=", WA";';
echo '}';
echo '}';
echo '</script>';

(It's included in a Wordpress Plugin, hence the echo tags)and the form itself:
PHP Code:
echo '<form method="post" action="http://'.$current_site->domain . $current_site->path.'home/activity-search" onSubmit="javascript:checkState();return true;">';
echo '<label>Suburb:</label><input type="text" name="address" id="suburb-address" title="Enter Suburb & State" />';
echo '<select name="categories[]" >';
echo '<option value ="">All Activities</option>';
$categories_list = split('[
]', get_setting('categories', $db));
foreach ($categories_list AS $cat){
$cat = trim($cat);
echo '<option>'.$cat.'</option>';
} echo '</select>';
echo '<label>Country:</label>';
echo '<select name="country" id="country">';
echo'<option>au</option>';
echo '</select>';
echo '<label>Radius:</label>';
echo '<select name="radius" id="radius">';
echo'<option>15</option>';
echo '</select>';
echo '<input type="submit" name="submit" value="Search" class="btn" />';
echo '</form>';
I'm wondering whether the if statement is valid, but I'm not knowledgeable in Javascript, so I don't know where to begin.