Bug 45926 – JSDatabase ResultSet.rows.item(pos) throws exception, but it should return null

• Status: UNCONFIRMED
• Component: WebCore JavaScript

[Matt Bishop]

A SQL query ResultSet rows object gives one access to the result rows of a query.  The way to access a particular row is by using this call:

    var aRow = resultSet.rows.item(rowPos);

If the rowPos indicates a row that is not in the row list, the method should return null.  For instance, if there are 5 rows but I ask for rows.item(10) I should get null.

Instead, I get an error: "INDEX_SIZE_ERR: DOM Exception 1: Index or size was negative, or greater than the allowed value."

This is according to the Web SQL Database spec (http://dev.w3.org/html5/webdatabase/#sqlresultsetrowlist).

WHY THIS IS IMPORTANT

The only way to safely iterate a resultset is like this:

var len = resultSet.rows.length;
for (int i = 0; i < len; i++) {
    var aRow = resultSet.rows.item(i);
    //process the row
}

Not bad, but rows.length should be avoided, as an implementation may need to scan the entire resultSet; if the resultSet is large, it can cause memory troubles, slowdowns, etc.  If the implementation of rows.item() is lazy, then length() need never be called.

The safer way to iterate is to do this:

var i = -1;
while ((aRow = resultSet.rows.item(++i)) != null) {
    //process the row
}

[Matt Bishop]

Created attachment 67849 [details]
HTML file showing bug.