What are you trying to achieve here?

mydata[0][0]

will give you the first character of the id field.
if you want only the id, it should be

mydata[0]

You can read more about arrays here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array

Also, while debugging, its better to use

console.log()

instead of

alert() 

as there are some restrictions on what it alert() will show. You can access the console by pressing ctrl+shift+i on chrome.

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