How many elements using jquery and php

You can't have the elements with the same id. Are you sure you have the elements with the same id?
To get the number of the elements use length:
Take this sample:

<input type='text' id='theSameIDName' name='theSameName'>
<input type='text' id='theSameIDName' name='theSameName'>

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And the following javascript code:

alert($("[name='theSameName']").length);

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alert($("#theSameIDName").length);

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The first alert will display 2, but the second one will display 1

You most definetalty can have elements with the same name...

jquery needs to be able to count elements... hopefully in a few years.  Lame

jQuery does:

alert($(':input').length);

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See here: https://api.jquery.com/input-selector/