JS读取文件大小，判断图片高宽

Checking a selected file's size requires local file system access which
is usually for web pages not possible due to security considerations.
If security settings are low enough NN4 can call into Java to read the
file's size, IE4+ can use the FileSystemObject to check the file's size.

The following page has two functions
getFileSize
and
getImageDimension
containing NN4 and IE4+ code to solve the described tasks.
IE安全有限制
用Web页面执行客户端程序
但必需客户端打开IE选项中的安全属情中的对没有标记为安全的ActiveX控件进行初始化和执行脚本
<HTML>
<HEAD>
<SCRIPT>
function getImageDimension (imgURL, loadHandler) {
var img = new Image();
img.onload = loadHandler;
if (document.layers
&& location.protocol.toLowerCase() != 'file:'
&& navigator.javaEnabled())
netscape.security.PrivilegeManager.enablePrivilege(
'UniversalFileRead'
);
img.src = imgURL;
}
function getFileSize (fileName) {
if (document.layers) {
if (navigator.javaEnabled()) {
var file = new java.io.File(fileName);
if (location.protocol.toLowerCase() != 'file:')
netscape.security.PrivilegeManager.enablePrivilege(
'UniversalFileRead'
);
return file.length();
}
else return -1;
}
else if (document.all) {
window.oldOnError = window.onerror;
window.onerror = function (err) {
if (err.indexOf('utomation') != -1) {
alert('file access not possible');
return true;
}
else
return false;
};
var fso = new ActiveXObject('Scripting.FileSystemObject');
var file = fso.GetFile(fileName);
window.onerror = window.oldOnError;
return file.Size;
}
}
function showImageDimensions () {
alert(this.width + 'x' + this.height);
}
</SCRIPT>
<SCRIPT>
function checkImageDimensions (fileName) {
var imgURL = 'file:///' + fileName;
getImageDimension(imgURL, showImageDimensions);
}
</SCRIPT>
</HEAD>
<BODY>
<FORM NAME="formName">
<INPUT TYPE="file" NAME="fileName">
<BR>
<INPUT TYPE="button" VALUE="check file size"
ONCLICK="alert(getFileSize(this.form.fileName.value))"
>
<BR>
<INPUT TYPE="button" VALUE="check image dimensions"
ONCLICK="checkImageDimensions(this.form.fileName.value)"
>
</FORM>
</BODY>
</HTML>