案例:javascript案例     状态:可编辑再运行    进入竖版
 运行结果 
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<!DOCTYPE html>
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<html>
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<body>
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<script>
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var person;
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var car="Volvo";
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document.write(person + "<br />");
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document.write(car + "<br />");
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var car=null
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document.write(car + "<br />");
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</script>
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</body>
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</html>
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