JS案例：通过typedof测试变量类型示例
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<title>typeof运算符测试示例</title>
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<script type="text/javascript">
var a,type_a;
a=100; type_a=typeof a; document.writeln("变量a的类型是："+type_a);
a=true; type_a=typeof a; document.writeln("变量a的类型是："+type_a);
a="hello"; type_a=typeof a; document.writeln("变量a的类型是："+type_a);
a=null; type_a=typeof a; document.writeln("变量a的类型是："+type_a);
</script>
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