JavaScript preview Local Picture

Javascript

<input id= "File" type= "file" >
<br/>

<script language= "javascript" type= "Text/javascript" >
//==============================
Features: JavaScript local picture preview
Author:yaosansi
Site:http://www.yaosansi.com
Date:2006-02-21
Description: Simple judgment of the legality of the document
Apply to: Preview local picture before uploading files
//==============================
function ShowImage (value,img)
{
alert (value);
Detection Letter
Alert (Value.indexof (': '));
Detect if file has an extension
Alert (Value.length-value.lastindexof ('. '));
Fetch file extension
Alert (VALUE.SUBSTR (value.length-3,3));
Detect if file name extension is legal
Alert (Checkext (VALUE.SUBSTR (value.length-3,3)));

if (Value.length>5&&value.indexof (': ') ==1&& (Value.length-value.lastindexof ('. ')) ==4&&checkext (Value.substr (value.length-3,3))
{
Img.src=value;
img.alt= "local picture preview";
img.style.visibility= "visible";
}
Else
{
Img.style.visibility= "hidden";
}
}
Check that the extension is legitimate and return true
function Checkext (EXT)
{
Set the allowed extensions here
var allowext= "Jpg|gif|jpeg|png|bmp";
var Extok=false;
var Arrayext;
if (Allowext.indexof (' | ')! =-1)
{
Arrayext=allowext.split (' | ');
for (i=0;i<arrayext.length;i++)
{
if (Ext.tolowercase () ==arrayext[i])
{
Extok=true;
Break
}
}
}
Else
{
Arrayext=allowext;
if (Ext.tolowercase () ==arrayext)
{
Extok=true;
}
}
return extok;
}
</script>