报错Uncaught ReferenceError: $ is not defined。对照视频码的代码，html中已经引用了，但是到网页就报错，是怎么回事
;$(function()
{
'use strict';
var sidebar=$('.sidebar'),
mask=$('.mask'),
sidebar_trigger=$('#sidebar_trigger');
function showsidebar()
{
mask.fadeIn();
sidebar.css('right',0);
}
function hidsidebar()
{
mask.fadeout();
sidebar.css('right',-sidebar.width());
}
sidebar_trigger.on('click',showsidebar)
mask.on('click',hidsidebar)
})
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;$(function()
{
'use strict';
var sidebar=$('#sidebar'),
mask=$('.mask'),
sidebar_trigger=$('#sidebar_trigger');
sidebar_trigger.on('click',function()
{
mask.fadeIn();
})
})
现在把class改成了id,只输入到这里就开始报同样的错，怎么回事
