How to hide a div using javascript

Question

I want to hide a div using Javascript. Below is my div.

Answer 1

That's not javascript, but jQuery:

You can simply use hide() method:

$(".ui-dialog-titlebar-close").hide(); // you can also use css() method as yours

And you need to wrap your code inside ready handler:

$(document).ready(function(){
//your code here
});

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You can learn more about jQuery here.