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#parent {600px; height:20px; background:#CCC; position:relative; margin:10px auto;}
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document.onmousemove=function (ev)
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document.title=scale;
oDiv3.style.top=-scale*(oDiv3.offsetHeight-oDiv2.offsetHeight)+'px';
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document.onmouseup=function ()
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第一部分: 入门课程、了解JavaScript - 案例+知识点，夯实基础做足准备
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