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JavaScript jQuery Basics (2014) Creating a Simple Lightbox Perform: Part 2

Confuse about $("<h1></h1>") equality in jQuery

As the teacher said in minute around 3:08. Instead of using the HTML tag for the .append(""), we mark is as a variable so that it could be used again easily.

Here is my own code, https://jsfiddle.net/fatihamzah/u5d0cfgj/

Instead of using: "<div id='overlay'></div>" We created: var $overlay = $("<div id='overlay'></div>"); Then we use: $overlay

From this.. $("body main").append("<div id='overlay'></div>"); To this... $("body main").append($overlay);

And we can do this.. $($overlay).fadeIn();

right? my question is:

Logically, this makes the $overlay is interchangable with $("<div id='overlay'></div>") ?? If so,,, why can't we do this...

$($("<div id='overlay'></div>")).fadeIn();

I think I know that it is because of the dollar sign and parenthesis $( ) right??

But why it is only work with $overlay?

What I knew is: var something = "string"

console.log(something) -is interchangable with...

console.log("string")

and both works.

  1. Can someone explain what is happening here, I just need a reason why it is like that... or is it just the 'magic' of jQuery?
  2. I still don't get in why it should be $( "string" ) instead of "string"

Thankyou!

1 Answer

Steven Parker
Steven Parker
229,982 Points

The jQuery() function does different things depending on the argument.

When you give it a string, it looks to see if the string starts with an HTML element tag and if so, it creates a new object. But if it finds a selector, it scans the document and returns an object that represents the matching elements(s). It can do other things also, see the jQuery documentation for full details.

In this example: var $overlay = $("<div id='overlay'></div>"); β€” a new object is created and assigned to the variable $overlay.

:x: $($overlay).fadeIn(); :point_left: You would not do this, since $overlay is already a jQuery object.
:white_check_mark: $overlay.fadeIn(); :point_left: You would do this instead.

Hopefully, that answers question 1. It's not "magic", it's polymorphism.

For question 2, "string" is just a string, no matter what the contents are; but $("string") would be a new jQuery object when the string contains an HTML tag.

ohh.. I see,, I wonder why I was come to a conclusion that $overlay.fadeIn(); would never worked.. but it actually works..

Thankyou very much!