Javascript setting value in session state

Question

I have a javascript that figures our the interest rate for a mortgage loan based on principal balance, term and monthly payment. The script also rounds up to the nearest 8th. Here is the line code that sets the value on the APEX form:
document.getElementById('P2_NOTE_RATE_TO_PITIA_31').value = cRate.toFixed(3);
Obviously this line code doesn't set session state for the value. Users have to submit the form again to pass this new rate to other calculations on the forms.
Is there another piece of code I need to add to force value to session state? The javascript is called via the page load and it will produce the correct rate when ever values are changed to warrant a new interest rate to be calculated.
Here is the entire javascript:
function loanrate() { 
function getVal(item){
if($x(item).value != "")
return parseFloat($x(item).value);
else
return 0 ;
//Allow rates of 0 to 100%, solve to the nearest 0.001%
var a=0.00001;
var b=1;
var tol=0.00001;
var test;
var t;
var y1;
var y2;
var P = getVal('P2_NEW_BAL_CALC');
var A = getVal('P2_NEW_PI_TARGET');
var N = getVal('P2_REMAINING_TERM');
var nRate;
var cRate;
var root;
var TEMP = a;
// Allow only 100 iterations (more than enough for convergence)
for(var k = 1; k<=100; k++) {
// A*(Math.pow((1+i),N)-1)/(i*Math.pow((1+i),N)) = present worth of N payments of A (beginning
// 1 period from now)
// Finally, subtract P (the present worth, or the price).
i = a;
y1 = A *(Math.pow((1+i),N)-1)/(i*Math.pow((1+i),N))- P;
i = b;
y2 = A *(Math.pow((1+i),N)-1)/(i*Math.pow((1+i),N))- P;
test = y1*y2;
// If test>0, the function that is to be driven to zero has the same sign
// for both sides of the interval.
if (test>0) {
b = a;
a = TEMP;
a = (a+b)/2;
} else {
// If test <0, the root of the equation is between a and b.
// If the interval is small enough, return (a+b)/2 as the root.
// If not, bisect the interval: save a as TEMP, move a (new) halfway toward b.
t = (b-a)/2;
if (t<tol) {
root = (a+b)/2;
// Compute the annual compounded rate, if payments are monthly
//var annual = 100*(Math.pow((1+root),12)-1);
root = root * 100;
nRate = Math.round(1000 * root)/1000 ;
cRate = (Math.ceil((nRate * 12)/.125)*.125);
document.getElementById('P2_NOTE_RATE_TO_PITIA_31').value = cRate.toFixed(3);
//$x_Value('P4_ANNUAL_RATE',Math.round(1000*annual)/1000);
break;
} else {
TEMP = a;
a = (a+b)/2;
}

Answer 1

I believe the following will do what you need.
document.getElementById('P2_NOTE_RATE_TO_PITIA_31').value = cRate.toFixed(3);
var get = new htmldb_Get(null,&APP_ID.,'APPLICATION_PROCESS=dummy',0);
get.add('P2_NOTE_RATE_TO_PITIA_31',$x('P2_NOTE_RATE_TO_PITIA_31').value)
gReturn = get.get();
...