Why does this syntax of $ for jQuery and Backbone.js work?

Question

For example, demo_view is an instance of Backbone.View, from this tutorial, this usage is recommended..

demo_view.$el.html()

As I understood, $ in jQuery is a function that should be used with parentheses, e.g. -> $("#id"), but why it can be used in demo_view.$el without a parentheses? Does anyone have ideas about this?

• Michael Geary: You've gotten some good answers, so this is just a fun tidbit to go with them. Paste this into the JavaScript console and see what happens: var π = Math.PI; alert(π); (Note that I'm not recommending that you use characters like this as variable names.)

Answer 1

It's also a symbol which can be used to name a simple variable, it belongs to the set of allowed characters for naming variables in javascript.

In jQuery, $ is used to name a function (it's a shorthand for the variable jQuery actually) but they could have chosen any letter of the alphabet or any other valid variable name.

Answer 2

The reason why they use $el is to denote that the el element is a jquery object. It is purely for readability. Appending '$' before a variable identifier is kind of like a notation that denotes that the variable is a jquery object.

Answer 3

Both $ and _ are valid symbols that can be used in variable names and property names. The convention by some develoepers is to use $ to indicate that the property or variable is a jQuery object and not some ordinary object or value. Thus you can readily tell that it is a jQuery object and use jQuery methods without doubt.