I'm learning jQuery by writing some code in Chrome's console, e.g. adding an id to a DOM element and then executing jQuery functions.
On some websites (for example Google) I get Uncaught TypeError and on others, I don't. Here is an example:
DOM modification:
<input id="test" aria-label="Szukaj w Google" name="btnK" type="submit" jsaction="sf.chk">
Console:
$("#test").hide()
Error:
VM598:1 Uncaught TypeError: $(...).hide is not a function
at <anonymous>:1:12
The same flow on other websites (for example StackOverflow) works. What is the reason?
jQuery is not loaded on many websites on the internet. That's why you get your error message Uncaught TypeError: $(...).hide is not a function, because actually the $ is not jQuery, rather another function, object, or it's just simply undefined.
Although you can find one of many versions of jQuery loaded on numerous websites, several companies/projects/websites don't use jQuery, or they use a custom build of it, or something else under the $ sign, or just not at all.
On a website, by default:
$ sign is an alias for document.querySelector()$$ sign is an alias for document.querySelectorAll()If that particular website doesn't override those variables with another implementation (e.g. custom function, library, jQuery, etc.). More on this
Credit to @AuxTaco
If you need to have jQuery on a website (e.g. for development purposes), where it's not present, you can inject it into the website.