input type=file的清空(javascript)

<input name="f1" value="C:\1.htm">
<input type="button" value="浏览" onClick="f2.click();f1.value=f2.value;">
<input type="file" id="f2" style="display:none">
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<script>
function cls(){
myfile.select();
document.execCommand("delete");
}
</script>

<input type=file name=myfile>
<input type=button onclick="cls()" value=清除>
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<input type="FILE" name="FILE1" size="50" value="这里为什麽显示不出来">
<script>
document.all.FILE1.focus();
var WshShell=new ActiveXObject("WScript.Shell");
WshShell.sendKeys("c:\\temp\\date.rar");
</script>
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<input type="file" name="file">
<input type="button" value="清除file里的内容" onclick="file.select();document
.selection.clear();">
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<form>
<input type="file">
<input type="button" value="清除file里的内容" onclick="form.reset()">
-----------------------------------------------
<input type="file" name="file">
<input type="button" value="清除file里的内容" onclick="file.outerHTML=file
.outerHTML">