//инпут рубля, спан юаня, кол-во рублей за юань, кол-во рублей за рубль

CurrencyConverter = function(idI, idS, currency1, currency2) {
	this.I = document.getElementById(idI);
	this.S = document.getElementById(idS);
	this.C1 = currency1;
	this.C2 = currency2 || 1;
	this.test();
}

CurrencyConverter.prototype.Calculate = function() {
	var v = parseFloat(this.I.value);
	var r = this.C2 * v / this.C1;
	this.S.innerHTML = r.toFixed(2);
} 

CurrencyConverter.prototype.test = function() {
	this.I.value = this.I.value.replace(/\,/g,"\.");
	if (this.I.value.match(/^\d+(\.\d*)?$/)) {
		this.I.className = CurrencyConverter.ClassCorrectValue;
		this.Calculate();
	} else {
		this.I.className = CurrencyConverter.ClassInvalidValue;			
	}
	if (this.I.value == '') this.S.innerHTML = '0.00';				
}

CurrencyConverter.ClassCorrectValue = "validTf";
CurrencyConverter.ClassInvalidValue = "invalidTf";