jQuery: Why prepend a $ to variable name?

I am trying to learn jQuery and I came across this line in an example.

var $title = $(tag).attr('title');

Can someone please tell me what the prepended $ is for in $title.

The example seems to work fine if I replace $title with just title.

I understand this is probably a stupid question but it is a waste of time googling for "purpose of $"

Ma开发者_如何学编程ny thanks.

It doesn't "mean" anything. The $ character is a legal character in Javascript variable names.

However, there is a convention (which isn't universal) of using $ as a prefix to any variable that points to a jQuery selection.

You give the example:

var $title = $(tag).attr('title');

This is a bad use of the $ character, according to this convention. $title is a string, not a jQuery selection.

This would be a correct use of the character:

var $el = $(tag);
var title = $el.attr('title');

Otherwise, a big reason for the prevalence of the $ character is that it is mandatory in PHP, and there is a big overlap between jQuery and PHP programmers.

I think people use it as a convention for 'things I looked up with jQuery that I want to hold onto without needing to look up again'.

The one you see most often is var $this = $(this)

$ is a valid character in javascript variable names. It makes no difference in the snipped you posted. See this related answer.

Looks like a PHP developer was getting a bit tired and didn't realise he was in a javaScript code block.

In JavaScript you don't need to have $ on variable names. However, to access the element using jQuery (usually by the $) you'll need the $ on the ('#selector_id') bit - i.e. $('#selector_id').

The intent of this is to denote to the programmer that the variable is a jQuery wrapper object.

In javascript $ is nothing. This is the same as add a to title (atitle). It's just a symbol you can use for names.

there is no purpose for $, it's just named that way. =)

The symbol '$' is mapped to the jQuery class. There is NO reason to prefix title with '$'.