In jQuery the variable is assigned a copy of the jQuery function. This function is heavily overloaded and means half a dozen different things depending on what arguments it is passed.
A '$' in a variable means nothing special to the interpreter, much like an underscore. From what I've seen, many people using jQuery (which is what your example code looks like to me) tend to prefix variables that contain a jQuery object with a $ so that they are easily identified and not mixed up with, say, integers. The dollar sign function $() in jQuery is a library function that is ...
The $ is an alias for jQuery which (jQuery) is a Javascript library. Plug-ins are usage of the library in a specific fashion which create specific use of the library and extend its functionality.
When you pass this to the jQuery constructor, you are passing the current element for a jQuery object to be constructed with. The jQuery object then contains an array-like structure of the DOM elements matching the selector (or just the single element in the case of this). Once the jQuery object is constructed, the jQuery API is now exposed.
When inside a jQuery method’s anonymous callback function, this is a reference to the current DOM element. $ (this) turns this into a jQuery object and exposes jQuery’s methods. A jQuery object is nothing more than a beefed-up array of DOM elements.
$("div.id_100 > select > option[value=" + value + "]").prop("selected",true); Where value is the value you wish to select by. If you need to removed any prior selected values, as would be the case if this is used multiple times you'd need to change it slightly so as to first remove the selected attribute
here is a code that is working: the jQuery will treat only the buttons that are of class .cls-hlpb, it will take the id of the button that was clicked and will change it according to the data that comes from the ajax.
In the following example the console shows "window loaded" before "document loaded" when using jQuery 3.4.1 but when using jQuery 2.2.4 it always works as expected ("document loaded" appears before "window loaded").
