Is there any reason to have nested calls to $ (jQuery)?
I was poking around the source code of a website when I came across some code like this:
$($('#newForm_step1')).hide("slide", { direction: "left" }, 0);
and this:
$($($('.breadcrumbs')[0]).children().last()).html("...");
I've never seen the $ ( jQuery ) function used this way, and I was wondering if there'd be any practical reason to do something like this? To the best of my knowledge, wrapping a jQuery object with a call to $ simply returns a jQuery object for the same selector, and methods on jQuery objects return this , so I don't see why one would need nested calls to $ .
No, there is no reason to do this.
In the first example, $($(...)) is redundant. There is absolutely no effect in immediately wrapping a jQuery object in another jQuery object.
The line should read
$('#newForm_step1').hide("slide", { direction: "left" }, 0);
In the second example, $(...)[0] returns a raw DOM element, so it's wrapped again before having jQuery's .children().last() invoked on it. The result of that is already a jQuery object, so there is no need to re-wrap it, and the "unwrapping" could have been avoided by calling .first() instead of [0] .
The line should read
$('.breadcrumbs').first().children().last().html("...");
There's no necessary to wrap jQuery object with jQuery. That will just result the same but over-coding and redundant.
But when you have DOM Object then you need to wrap with jQuery so that it will be jQuery object.
Taking your example:
$('.breadcrumbs')[0];//[0] converts to JavaScript Object
Now, if you want to work with jQuery again, you may then wrap with jQuery:
$($('.breadcrumbs')[0]);//is now a jQuery Object
But with this example is unnecessary because you can do just like this:
$('.breadcrumbs:eq(0)');//selects first .breadcrumbs element
However, if you have some DOM Object rather than jQuery object then you need jQuery wrapper to work with jQuery methods.
You must remember this:
JavaScript Object needs JavaScript methods to be chained:
javascriptObject.javascriptMethods
Ex-
$('.breadcrumbs')[0].addEventListener();//javascript addEventListener method
jQuery Object needs jQuery methods to be chained:
jQueryObject.jQueryMethods
Ex-
$('.breadcrumbs').on();//jQuery on method
上一篇: 序列化不带引号的属性名称