Check if a file exists locally using JavaScript on

问题:

I want to check if a file exists locally, where the HTML file is located. It has to be JavaScript. JavaScript will never be disabled. jQuery is not good but can do.

By the way, I am making a titanium app for Mac so I am looking for a way of protecting my files from people who click "show package contents".

回答1:

Your question is ambiguous, so there are multiple possible answers depending on what you're really trying to achieve.

If you're developping as I'm guessing a desktop application using Titanium, then you can use the FileSystem module's getFile to get the file object, then check if it exists using the exists method.

Here's an example taken from the Appcelerator website:

var homeDir = Titanium.Filesystem.getUserDirectory();
var mySampleFile = Titanium.Filesystem.getFile(homeDir, 'sample.txt');

if (mySampleFile.exists()) {
    alert('A file called sample.txt already exists in your home directory.');
    ...
}

Check the getFile method reference documentation

And the exists method reference documentation

For those who thought that he was asking about an usual Web development situation, then thse are the two answers I'd have given:

1) you want to check if a server-side file exists. In this case you can use an ajax request try and get the file and react upon the received answer. Although, be aware that you can only check for files that are exposed by your web server. A better approach would be to write a server-side script (e.g., php) that would do the check for you, given a filename and call that script via ajax. Also, be aware that you could very easily create a security hole in your application/server if you're not careful enough.

2) you want to check if a client-side file exists. In this case, as pointed you by others, it is not allowed for security reasons (although IE allowed this in the past via ActiveX and the Scripting.FileSystemObject class) and it's fine like that (nobody wants you to be able to go through their files), so forget about this.

回答2:

Since 'Kranu' helpfully advises 'The only interaction with the filesystem is with loading js files . . .', that suggests doing so with error checking would at least tell you if the file does not exist - which may be sufficient for your purposes?

From a local machine, you can check whether a file does not exist by attempting to load it as an external script then checking for an error. For example:

<span>File exists? </span>
<SCRIPT>
    function get_error(x){
        document.getElementsByTagName('span')[0].innerHTML+=x+" does not exist.";
    }
    url="   (put your path/file name in here)    ";
    url+="?"+new Date().getTime()+Math.floor(Math.random()*1000000);
    var el=document.createElement('script');
    el.id="123";
    el.onerror=function(){if(el.onerror)get_error(this.id)}
    el.src=url;
    document.body.appendChild(el);
</SCRIPT>

Some notes...

• append some random data to the file name (url+="?"+new Date etc) so that the browser cache doesn't serve an old result.
• set a unique element id (el.id=) if you're using this in a loop, so that the get_error function can reference the correct item.
• setting the onerror (el.onerror=function) line is a tad complex because one needs it to call the get_error function AND pass el.id - if just a normal reference to the function (eg: el.onerror=get_error) were set, then no el.id parameter could be passed.
• remember that this only checks if a file does not exist.

回答3:

You can use this

function LinkCheck(url)
{
    var http = new XMLHttpRequest();
    http.open('HEAD', url, false);
    http.send();
    return http.status!=404;
}

回答4:

Javascript cannot access the filesystem and check for existence. The only interaction with the filesystem is with loading js files and images (png/gif/etc).

Javascript is not the task for this

回答5:

Fortunately, it's not possible (for security reasons) to access client-side filesystem with standard JS. Some proprietary solutions exist though (like Microsoft's IE-only ActiveX component).

回答6:

If you want to check if file exists using javascript then no, as far as I know, javascript has no access to file system due to security reasons.. But as for me it is not clear enough what are you trying to do..

回答7:

An alternative: you can use a "hidden" applet element which implements this exist-check using a privileged action object and override your run method by:

File file = new File(yourPath);
return file.exists();

回答8:

One way I've found to do this is to create an img tag and set the src attribute to the file you are looking for. The onload or onerror of the img element will fire based on whether the file exists. You can't load any data using this method, but you can determine if a particular file exists or not.

回答9:

Try this:

window.onclick=(function(){
  try {
    var file = window.open("file://mnt/sdcard/download/Click.ogg");
    setTimeout('file.close()', 100);
    setTimeout("alert('Audio file found. Have a nice day!');", 101);
  } catch(err) {
    var wantstodl=confirm("Warning:\n the file, Click.ogg is not found.\n do you want to download it?\n "+err.message);
    if (wantstodl) {
      window.open("https://www.dropbox.com/s/qs9v6g2vru32xoe/Click.ogg?dl=1"); //downloads the audio file
    }
  }
});