Question

I have come across the following jQuery code but could not understand it. What does the following code, specially the “$([])” part in the last line mean ?

var instrument = $("#instrument"),
    quantity = $("#quantity"),
    orderType = $("#orderType"),
    price = $("#price"),
    validityDate = $("#validityDate"),
    allFields = $([]).add(instrument).add(quantity).add(orderType).add(price).add(validityDate)

Answer 1

Looks like it’s defining an array, then add()ing the DOM elements to it. From the manual:

Given a jQuery object that represents
a set of DOM elements, the .add()
method constructs a new jQuery object
from the union of those elements and
the ones passed into the method. The
argument to .add() can be pretty much
anything that $() accepts, including a
jQuery selector expression, references
to DOM elements, or an HTML snippet.

[] is an empty javascript array. As frunsi notes, this is not correct usage, and the [] definition is not required to create an empty set of elements, in 1.4 $() will do ths for you.