formChecker obect class

// for getElementById
function $lm(obj){
  if ( document.getElementById(obj) ) return document.getElementById(obj);
  else return false;
}

// first child of the same class
function firstChildofClass(p,cl) {
  if (!p || !p.childNodes.length)return;
  var ch = p.childNodes;
  for ( var i = 0; i < ch.length; i++ ){
    if (gotClass(ch[i],cl))return ch[i];
  }
  return;
}

// for firstChildOfClass
function $fc(p, cl){
  return firstChildofClass(p,cl);
}

// checks if object has the defined class
function gotClass(obj,cl) {
    var r = new RegExp("\\b" + cl + "\\b", "i");
    var ob = ( typeof(obj) == "object" ) ? obj : $lm(obj);
    if ( ob && ob.className && ob.className.match(r) !== null ) return true;
    return false;
}

function getChildElementsByClassName(obj,cl){
  var oc = ( obj != undefined ) ? obj.childNodes : document.body.childNodes;
  var ch = [];
  for ( var i = 0; i < oc.length; i++ ){
    if (gotClass(oc[i],cl)) ch.push(oc[i]);
  }
  return ch;
}

// for getChildElementsByClassName
function $cc(obj,cl){
  return getChildElementsByClassName(obj,cl);
}

function pf(n){return parseFloat(n);}

/* formChecker class definition
 * parameters:
 * fm - the form to be verified
 * rule - form rules in JSON format
 * rule record (object) properties:
 * sbj - input class
 *      if the form contains more than one input of the same class, each one will be verified
 * fnc - verifier function (these are methods of the chk() object class)
 *      see functions for more details
 * prm - value to verify against
 *      can be a fixed value or a form elem value defined by class or id (css-like definitions -> ".myclass" or "#myid")
 *
 * usage:
 *      1) link this script in your html head under some name (e.g. rule.js)
 *      2) insert the following script type="text/javascript" tag into your html head
 *      3) design your own rules
 *      4) design your own checker functions into the chk() class definition if necessary
 *
 * code into your html head:
 *
  window.onload = function(){

    // the form's send button input
    var sn = $lm("send");
    // the form dom object to be verified
    var fm = $lm("fm");
    // log div object to hold the verification result
    var lg = $lm("log");

    // send button event handler
    sn.onclick = function(){
        lg.innerHTML = "";
        var fc = new formChecker(fm,myRule);
        lg.innerHTML += fc.out();
    }
}

some rule examples:

myRule = {

    first: {
      sbj: "nm",
      fnc: "nn",
      prm: "",
      msg: "Name fields can not be empty."
    },

    second: {
      sbj: "yr",
      fnc: "gt",
      prm: ".minyr",
      msg: "Must be over 18."
    },

    third: {
      sbj: "yr",
      fnc: "lt",
      prm: "#maxyr",
      msg: "Must be under 99."
    },

    fourth: {
      sbj: "cn",
      fnc: "nn",
      prm: "",
      msg: "Can not be empty."
    },

    fifth: {
      sbj: "cn",
      fnc: "rg",
      prm: ["^hu$","i"],
      msg: "Must be hungarian."
    },

    sixth: {
      sbj: "cn",
      fnc: "ex",
      prm: "hu",
      msg: "Must be hungarian."
    },

    seventh: {
      sbj: "cn",
      fnc: "dd",
      prm: "hu",
      msg: "Errorous rule (no chk object method "dd")."
    }

  }


 *
**/

function formChecker(fm,rule){

    if (!fm) return;

    this.fm = fm;       // form DOM object
    this.rule = rule;   // rule JSON object-list
    this.res = [];      // result array

    this.chk = function(){

        var r,val,lm,c,prm;

        // rules
        for (var i in this.rule){

            r = this.rule[i];

            // check only if object exists
            if ( $fc(this.fm,r.sbj) ){

                // handle parameters
                // only try to find css-like object reference, if not number and not regexp
                // css-style DOM reference lookup with ".myclass" and "#myid"

                prm = r.prm;

                if ( isNaN(prm) && r.fnc != "rg" ){

                    // ".myclass"
                    if ( prm.match(/^\.\w+$/i) != null ){

                        var tst = true;
                        // only first object of the same class
                        if ( $fc( this.fm , prm.substr(1) ) )prm = $fc( this.fm , prm.substr(1) ).value;

                    }

                    // "#myid"
                    else if ( /^#\w+$/i.test(prm) ){

                        var tst = true;
                        if ( $lm( prm.substr(1) ) )prm = $lm( prm.substr(1) ).value;

                    }

                }

                // if there's more than one input of the same class, verify each
                lm = $cc(this.fm,r.sbj);
                for (var i in lm){

                    c = new chk(lm[i]);
                    try{

                        val = c.exec(r.fnc,prm);
                        if (!val)val = r.msg;
                        else val = "ok";

                    }catch(er){

                        val = er;

                    }

                    // uncomment below for debug
                    //val +=  " (prm: " + prm + " , tst: " + tst + ")";
                    this.res.push(val);

                }

            }

        }

    }

    // output
    this.out = function(){

        if (this.res.length < 1)this.chk();

        var s = "";
        for(var i = 0; i < this.res.length; i++ ){

            if(this.res[i] != true)s += this.res[i] + "<br>";

        }

        return s;

    }

}

function chk(obj){

    this.v = (obj.value) ? obj.value : obj.innerHTML;

    // numeric "equals"
    this.eq = function(b){
        if (pf(this.v) == pf(b))return true;
        return false;
    }

    // string equals ("exact")
    this.ex = function(b){
      if (this.v == b)return true;
      return false;
    }

    // numeric "lesser than"
    this.lt = function(b){
        if (pf(this.v) < pf(b))return true;
        return false;
    }

    // numeric "lesser or equals"
    this.le = function(b){
      if (pf(this.v) <= pf(b))return true;
        return false;
    }

    // numeric "greater than"
    this.gt = function(b){
      if (pf(this.v) > pf(b))return true;
        return false;
    }

    // numeric "greater or equals"
    this.ge = function(b){
      if (pf(this.v) >= pf(b))return true;
        return false;
    }

    // empty ?
    this.nn = function(){
        if (this.v.toString().length > 0)return true;
        return false;
    }

    // regexp pattern
    this.rg = function(b){
        var bb = new RegExp(b[0],b[1]);
        return bb.test(this.v);
    }

    this.exec = function(f, arg) {

        return this[f](arg);

    }

}