Question

If so, what is it?

I don’t mind if it involves using an external library.

Answer 1

Here (broken – Alternative location @ Google Code) is a jQuery plugin that implements the functionality.

_{Original page mirror on the Wayback Machine.}

The plugin code was also at the mirror:

/*##############################################################################
#    ____________________________________________________________________
#   /                                                                    \
#  |               ____  __      ___          _____  /     ___    ___     |
#  |     ____       /  \/  \  ' /   \      / /      /__   /   \  /   \    |
#  |    / _  \     /   /   / / /    /  ___/  \__   /     /____/ /    /    |
#  |   / |_  /    /   /   / / /    / /   /      \ /     /      /____/     |
#  |   \____/    /   /    \/_/    /  \__/  _____/ \__/  \___/ /           |
#  |                                                         /            |
#  |                                                                      |
#  |   Copyright (c) 2007                             MindStep SCOP SARL  |
#  |   Herve Masson                                                       |
#  |                                                                      |
#  |      www.mindstep.com                              www.mjslib.com    |
#  |   [e-mail]                           [e-mail]  |
#   \____________________________________________________________________/
#
#  Version: 1.0.0
#
#  (Svn version: $Id: jquery.printf.js 3434 2007-08-27 09:31:20Z herve $)
#
#----------[This product is distributed under a BSD license]-----------------
#
#  Redistribution and use in source and binary forms, with or without
#  modification, are permitted provided that the following conditions
#  are met:
#
#     1. Redistributions of source code must retain the above copyright
#        notice, this list of conditions and the following disclaimer.
#
#     2. Redistributions in binary form must reproduce the above copyright
#        notice, this list of conditions and the following disclaimer in
#        the documentation and/or other materials provided with the
#        distribution.
#
#  THIS SOFTWARE IS PROVIDED BY THE MINDSTEP CORP PROJECT ``AS IS'' AND
#  ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
#  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
#  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MINDSTEP CORP OR CONTRIBUTORS
#  BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
#  OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
#  OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
#  BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
#  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
#  OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
#  EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
#  The views and conclusions contained in the software and documentation
#  are those of the authors and should not be interpreted as representing
#  official policies, either expressed or implied, of MindStep Corp.
#
################################################################################
#
#   This is a jQuery [jquery.com] plugin that implements printf' like functions
#   (Examples and documentation at: http://mjslib.com)
#
#   @author: Herve Masson
#   @version: 1.0.0 (8/27/2007)
#   @requires jQuery v1.1.2 or later
#   
#   (Based on the legacy mjslib.org framework)
#
##############################################################################*/

(function($) {

    /*
    **  Just an equivalent of the corresponding libc function
    **
    **  var str=jQuery.sprintf("%010d %-10s",intvalue,strvalue);
    **
    */

    $.sprintf=function(fmt)
    {
        return _sprintf_(fmt,arguments,1);
    }


    /*
    **  vsprintf takes an argument list instead of a list of arguments (duh!)
    **  (useful when forwarding parameters from one of your functions to a printf call)
    **
    **  str=jQuery.vsprintf(parameters[,offset]);
    **
    **      The 'offset' value, when present, instructs vprintf to start at the
    **      corresponding index in the parameter list instead, of 0
    **
    **  Example 1:
    **
    **      function myprintf(<printf like arguments>)
    **      {
    **          var str=jQuery.vsprintf(arguments);
    **          ..
    **      }
    **      myprintf("illegal value : %s",somevalue);
    **
    **
    **  Example 2:
    **
    **      function logit(level,<the rest is printf like arguments>)
    **      {
    **          var str=jQuery.vsprintf(arguments,1);   // Skip prm #1
    **          ..
    **      }
    **      logit("error","illegal value : %s",somevalue);
    **
    */

    $.vsprintf=function(args,offset)
    {
        if(offset === undefined)
        {
            offset=0;
        }
        return _sprintf_(args[offset],args,offset+1);
    }


    /*
    **  logging using formatted messages
    **  ================================
    **
    **  If you _hate_ debugging with alert() as much as I do, you might find the
    **  following routines valuable.
    **
    **  jQuery.alertf("The variable 'str' contains: '%s'",str);
    **      Show an alert message with a printf-like argument.
    **
    **  jQuery.logf("This is a log message, time is: %d",(new Date()).getTime());
    **      Log the message on the console with the info level
    **
    **  jQuery.errorf("The given value (%d) is erroneous",avalue);
    **      Log the message on the console with the error level
    **
    */

    $.alertf=function()
    {
        return alert($.vsprintf(arguments));
    }

    $.vlogf=function(args)
    {
        if("console" in window)
        {
            console.info($.vsprintf(args));
        }
    }

    $.verrorf=function(args)
    {
        if("console" in window)
        {
            console.error($.vsprintf(args));
        }
    }

    $.errorf=function()
    {
        $.verrorf(arguments);
    }

    $.logf=function()
    {
        $.vlogf(arguments);
    }


    /*-------------------------------------------------------------------------------------------
    **
    **  Following code is private; don't use it directly !
    **
    **-----------------------------------------------------------------------------------------*/

    FREGEXP = /^([^%]*)%([-+])?(0)?(\d+)?(\.(\d+))?([doxXcsf])(.*)$/;
    HDIGITS = ["0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"];

    function _empty(str)
    {
        if(str===undefined || str===null)
        {
            return true;
        }
        return (str == "") ? true : false;
    }

    function _int_(val)
    {
        return Math.floor(val);
    }

    function _printf_num_(val,base,pad,sign,width)
    {
        val=parseInt(val,10);
        if(isNaN(val))
        {
            return "NaN";
        }
        aval=(val<0)?-val:val;
        var ret="";

        if(aval==0)
        {
            ret="0";
        }
        else
        {
            while(aval>0)
            {
                ret=HDIGITS[aval%base]+ret;
                aval=_int_(aval/base);
            }
        }
        if(val<0)
        {
            ret="-"+ret;
        }
        if(sign=="-")
        {
            pad=" ";
        }
        return _printf_str_(ret,pad,sign,width,-1);
    }

    function _printf_float_(val,base,pad,sign,prec)
    {
        if(prec==undefined)
        {
            if(parseInt(val) != val)
            {
                // No decimal part and no precision -> use int formatting
                return ""+val;
            }
            prec=5;
        }

        var p10=Math.pow(10,prec);
        var ival=""+Math.round(val*p10);
        var ilen=ival.length-prec;
        if(ilen==0)
        {
            return "0."+ival.substr(ilen,prec);
        }
        return ival.substr(0,ilen)+"."+ival.substr(ilen,prec);
    }

    function _printf_str_(val,pad,sign,width,prec)
    {
        var npad;

        if(val === undefined)
        {
            return "(undefined)";
        }
        if(val === null)
        {
            return "(null)";
        }
        if((npad=width-val.length)>0)
        {
            if(sign=="-")
            {
                while(npad>0)
                {
                    val+=pad;
                    npad--;
                }
            }
            else
            {
                while(npad>0)
                {
                    val=pad+val;
                    npad--;
                }
            }
        }
        if(prec>0)
        {
            return val.substr(0,prec);
        }
        return val;
    }

    function _sprintf_(fmt,av,index)
    {
        var output="";
        var i,m,line,match;

        line=fmt.split("\n");
        for(i=0;i<line.length;i++)
        {
            if(i>0)
            {
                output+="\n";
            }
            fmt=line[i];
            while(match=FREGEXP.exec(fmt))
            {
                var sign="";
                var pad=" ";

                if(!_empty(match[1])) // the left part
                {
                    // You can't add this blindly because mozilla set the value to <undefined> when
                    // there is no match, and we don't want the "undefined" string be returned !
                    output+=match[1];
                }
                if(!_empty(match[2])) // the sign (like in %-15s)
                {
                    sign=match[2];
                }
                if(!_empty(match[3])) // the "0" char for padding (like in %03d)
                {
                    pad="0";
                }

                var width=match[4]; // the with (32 in %032d)
                var prec=match[6];  // the precision (10 in %.10s)
                var type=match[7];  // the parameter type

                fmt=match[8];

                if(index>=av.length)
                {
                    output += "[missing parameter for type '"+type+"']";
                    continue;
                }

                var val=av[index++];

                switch(type)
                {
                case "d":
                    output += _printf_num_(val,10,pad,sign,width);
                    break;
                case "o":
                    output += _printf_num_(val,8,pad,sign,width);
                    break;
                case "x":
                    output += _printf_num_(val,16,pad,sign,width);
                    break;
                case "X":
                    output += _printf_num_(val,16,pad,sign,width).toUpperCase();
                    break;
                case "c":
                    output += String.fromCharCode(parseInt(val,10));
                    break;
                case "s":
                    output += _printf_str_(val,pad,sign,width,prec);
                    break;
                case "f":
                    output += _printf_float_(val,pad,sign,width,prec);
                    break;
                default:
                    output += "[unknown format '"+type+"']";
                    break;
                }
            }
            output+=fmt;
        }
        return output;
    }

})(jQuery);