Question

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What does the second argument to $() mean?

There is some time that i use jQuery and from time to time I see this:

$(argument1, argument2).doSomething();

Where is the documentation for filtering with a second argument?

EDIT:

I’m talking about this way of using it:

var t=0; // the height of the highest element (after the function runs)
var t_elem;  // the highest element (after the function runs)
$("*",elem).each(function () {
    $this = $(this);
    if ( $this.outerHeight() > t ) {
        t_elem=this;
        t=$this.outerHeight();
    }
});

Notice:

$("*",elem)

I’m not talking about

$("a,b,span")

way of filtering. I now that well.

Answer 1

It’s the first definition in the jQuery() documentation:

jQuery( selector [, context ] )

   selector
      Type: selector
      A string containing a selector expression

   context
      Type: Element, jQuery
      A DOM Element, Document, or jQuery to use as context

and further down:

Selector Context

By default, selectors perform their searches within the DOM starting at the document root. However, an alternate context can be given for the search by using the optional second parameter to the $() function.

However, internally it just calls .find and you will often find people recommending the usage of .find over passing a second argument.

So, your example is equivalent to $(argument2).find(argument1).doSomething();