这是一个计算器,您可以参考。
去Javascript源码,可以发现计算未来值的公式是这样的:
function checkNumber(input, min, max, msg)
{
msg = msg + " field has invalid data: " + input.value;
var str = input.value;
for (var i = 0; i < str.length; i++) {
var ch = str.substring(i, i + 1)
if ((ch < "0" || "9" < ch) && ch != '.') {
alert(msg);
return false;
}
}
var num = 0 + str
if (num < min || max < num) {
alert(msg + " not in range [" + min + ".." + max + "]");
return false;
}
input.value = str;
return true;
}
function computeField(input)
{
if (input.value != null && input.value.length != 0)
input.value = "" + eval(input.value);
computeForm(input.form);
}
function computeForm(form)
{
if ((form.payments.value == null || form.payments.value.length == 0) ||
(form.interest.value == null || form.interest.value.length == 0) ||
(form.principal.value == null || form.principal.value.length == 0)) {
return;
}
if (!checkNumber(form.payments, 1, 480, "# of payments") ||
!checkNumber(form.interest, .001, 99, "Interest") ||
!checkNumber(form.principal, 1, 10000000, "Principal")) {
form.fv.value = "Invalid";
return;
}
var i = form.interest.value;
if (i > 1.0) {
i = i / 100.0;
form.interest.value = i;
}
i /= 12;
var pow = form.principal.value;
for (var j = 0; j < form.payments.value *12; j++)
pow = (pow * i) + (pow *1);
form.fv.value = pow
form.totalint.value = (form.fv.value - form.principal.value)
}