Selecting the first "n" items with jQuery

You probably want to read up on slice. Your code will look something like this:

$("a").slice(0,20)

Use lt pseudo selector:

$("a:lt(n)")

This matches the elements before the nth one (the nth element excluded). Numbering starts from 0.

I found this note in the end of the lt() docs:

Additional Notes:
Because :lt() is a jQuery extension and not part of the CSS specification, queries using :lt() cannot take advantage of the performance boost provided by the native DOM querySelectorAll() method. For better performance in modern browsers, use $("your-pure-css-selector").slice(0, index) instead.

So use $("selector").slice(from, to) for better performances.