问题
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Why would a javascript variable start with a dollar sign?
I see people using the dollar sign in front of variables when using jQuery. Is there any reason behind this? I\'m I missing something basic or is it just a common practice?
回答1:
It's a common reference to a jQuery wrapped object. It makes reading the code easier to know which variables are jQuery wrapped.
//Item has been "cached" for later use in the script as a jQuery object.
var $item = $(this);
回答2:
For me a common practice is this:
If a variable is private I use an underscore like this:
(function(){
var _foo = "bar";
})()If it's public I'll use no underscore:
var foo = "bar"And if it's a jQuery selector I'll use the $:
var $foo = $('bar');
//then you can access it like this
$foo.attr('id')It's just coding convention and it allows you to quickly reference what type the variable is later in the code.
回答3:
Many people using jQuery will prefix variables that contain a jQuery object with a $, so that they are easily identified. Consider this example:
var $img = $(".someclass span.otherclass img");
/* somewhere later in the code */
$img.bind("click", function() {/*...*/});
回答4:
In my experience this is just a readability. Some developers like to prefix their variables so that they are easy to spot. It could also be a PHP habit creeping it's way in to Javascript.
回答5:
Dollar signs in code that uses JQuery commonly means that the variable in question is a jQuery variable (an object wrapped by jquery).
来源：https://stackoverflow.com/questions/6209462/when-why-to-prefix-variables-with-when-using-jquery