Let's say that I send a JS array to a php page using an http post:
var tags = ['foo', 'bar'];
My goal is to do a new INSERT in my db table for each tag (because I suppose I can't insert multiple rows with one query)? How do I loop through the array and insert the values in to the table using mysql_query?
Send the post parameters in form tags[]=foo&tags[]=bar. PHP should receive them as a $_REQUEST['tags'] array. Then iterate as normal in PHP.
Alternately, use JSON.stringify(thing) on clientside to get a string representation you can send as a single parameter, then restore it with json_decode(param) on PHP side - and again you get a PHP array.
You can iterate a PHP array using the foreach ($array as $element) { ... } construct.
Also, you can insert multiple rows with one INSERT:
INSERT INTO mytable (col1, col2)
VALUES
('foo', 'bar'),
('baz', 'moo')
