<!-- This example is from the book _JavaScript: The Definitive Guide_. -->
<!-- Written by David Flanagan. Copyright (c) 1996 O'Reilly & Associates. -->
<!-- This example is provided WITHOUT WARRANTY either expressed or implied.-->
<!-- You may study, use, modify, and distribute it for any purpose. -->
<HEAD>
<TITLE>1996 U.S. Federal Income Tax Estimator</TITLE>
<SCRIPT>
// These functions define the data structures we'll use to store
// tax bracket and tax schedule data for computing taxes.
function TaxBracket(cutoff, percentage, base)
{
this.cutoff =index.html cutoff; // how much money to be in this bracket
this.percentage = percentage; // what the tax is in this bracket
this.base = base; // combined tax from all lower brackets
}
function TaxSchedule(b0, b1, b2, b3, b4)
{ // A tax schedule is just 5 brackets
this[0] = b0; this[1] = b1; this[2] = b2; this[3] = b3; this[4] = b4;
}
// Taxes are computed using a tax schedule that depends on your filing status,
// so we create an array and store four different schedules in it.
var Schedules = new Object(); // create the array.
// Schedule X: Single
Schedules[0] = new TaxSchedule(new TaxBracket(263750, .396, 84020.5),
new TaxBracket(121300, .36, 32738.5), new TaxBracket(58150, .31, 13162),
new TaxBracket(24000, .28, 3600), new TaxBracket(0, .15, 0));
// Schedule Z: Head of Household
Schedules[1] = new TaxSchedule(new TaxBracket(263750, .396, 81554),
new TaxBracket(134500, .36, 35024), new TaxBracket(83050, .31, 19074.5),
new TaxBracket(32150, .28, 4822.5), new TaxBracket(0, .15, 0));
// Schedule Y1: Married, Filing Jointly
Schedules[2] = new TaxSchedule(new TaxBracket(263750, .396, 79445),
new TaxBracket(147700, .36, 37667), new TaxBracket(96900, .31, 21919),
new TaxBracket(40100, .28, 6015), new TaxBracket(0, .15, 0));
// Schedule Y2: Married, Filing Separately
Schedules[3] = new TaxSchedule(new TaxBracket(131875, .396, 39722.5),
new TaxBracket(73850, .36, 18833.5), new TaxBracket(48450, .31, 10959.5),
new TaxBracket(20050, .28, 3007.5), new TaxBracket(0, .15, 0));
// The standard deduction allowed by tax law depends on filing status,
// so we've got to store this data in an array as well.
var StandardDeductions = new Object();
StandardDeductions[0] = 4000; StandardDeductions[1] = 5900;
StandardDeductions[2] = 6700; StandardDeductions[3] = 3350;
// This function computes the tax and updates all the elements in the form.
// It is triggered whenever anything changes, and makes sure that
// all elements of the form contains legal values and are consistent.
function compute(f)
{
var f = document.taxcalc; // This is the form we'll we working with;
// get the filing status
var status = f.status.selectedIndex;
// line 1, adjusted gross income
var income = parseFloat(f.income.value);
if (isNaN(income)) { income = 0; f.income.value = "0"; }
f.income.value = Math.round(income);
// line 2, the standard or itemized deduction
var deduction;
if (f.standard.checked)
deduction = StandardDeductions[status];
else {
deduction = parseFloat(f.deduction.value);
if (isNaN(deduction)) deduction = 0;
if (deduction < StandardDeductions[status]) {
deduction =index.html StandardDeductions[status];
f.standard.checked = true;
}
}
f.deduction.value = Math.round(deduction);
// Line 3: Subtract line 2 from line 1
var line3 = income - deduction;
if (line3 < 0) line3 =index.html 0;
f.line3.value = line3;
// Line 4: exemptions
var num_exemptions = parseInt(f.num_exemptions.value);
if (isNaN(num_exemptions)) num_exemptions = 1;
f.num_exemptions.value = num_exemptions;
var exemption = num_exemptions * 2550;
f.exemption.value = exemption;
// Line 5: subtract Line 4 from Line 3.
var line5 = line3 - exemption;
if (line5 < 0) line5 =index.html 0;
f.line5.value = line5;
// Line 6: tax from schedules.
// determine which tax schedule to use, based on filing status
var schedule = Schedules[status];
// determine which tax bracket to use within that schedule
for(var i = 0; i < 5; i++) if (line5 >=index.html schedule[i].cutoff) break;
var bracket = schedule[i];
// then compute the tax based on that bracket
var tax = (line5 - bracket.cutoff) * bracket.percentage + bracket.base;
f.tax.value = Math.round(tax);
}
</SCRIPT>
</HEAD>
<BODY>
<H1>1996 U.S. Federal Income Tax Estimator</H1>
To compute your 1996 U.S. Federal Income Tax, follow the steps in the
table below. You only need to enter the data in the boldface fields.
JavaScript will perform all the necessary computations for you.
<P>
<I>This program is an example only. Computing your actual income tax is
almost always more complicated than this!</I>
<!--
-- The stuff below is an HTML table inside of an HTML form. It gets tricky!
-- Notice the event handlers on all the form input elements.
-->
<FORM NAME="taxcalc">
<TABLE BORDER CELLPADDING=3>
<TR> <!-- Filing status -->
<TD> </TD>
<TD COLSPAN=3 BGCOLOR="d0d0d0">
<B>Select your filing status:</B>
<SELECT NAME="status" onChange="compute()">
<OPTION VALUE=0 SELECTED>Single
<OPTION VALUE=1>Head of Household
<OPTION VALUE=2>Married, Filing Jointly
<OPTION VALUE=3>Married, Filing Separately
</SELECT>
<TD></TR>
<TR> <!-- Line 1: Income -->
<TD>1.</TD>
<TD BGCOLOR="d0d0d0"><B>Enter your Adjusted Gross Income</B></TD>
<TD BGCOLOR="d0d0d0">
<INPUT TYPE=text NAME="income" SIZE=12 onChange="compute()">
</TD></TR>
<TR> <!-- Line 2: Deduction -->
<TD>2.</TD>
<TD BGCOLOR="d0d0d0">
<B>Check here
<INPUT TYPE=checkbox NAME="standard" CHECKED onClick="compute()">
for the standard deduction,<BR>or enter your Itemized Deduction</B>
</TD>
<TD BGCOLOR="d0d0d0">
<INPUT TYPE=text NAME="deduction" SIZE=12
onChange="this.form.standard.checked =index.html false; compute()">
</TD></TR>
<TR> <!-- Line 3: subtraction -->
<TD>3.</TD>
<TD>Subtract Line 2 from Line 1:</TD>
<TD><INPUT TYPE=text NAME="line3" SIZE=12 onChange="compute()"></TD></TR>
<TR> <!-- Line 4: Exemption -->
<TD ROWSPAN=2>4.</TD>
<TD BGCOLOR="d0d0d0">
<B>Enter your number of exemptions: </B>
<INPUT TYPE=text NAME="num_exemptions" SIZE=2 onChange="compute()">
</TD><TD></TD></TR>
<TR> <!-- Line 4, continued -->
<TD>Multiply number of exemptions by $2,550.</TD>
<TD><INPUT TYPE=text NAME="exemption" SIZE=12 onChange="compute()"></TD>
</TR>
<TR> <!-- Line 5: subtraction -->
<TD>5.</TD>
<TD>Subtract Line 4 from Line 3.</TD>
<TD><INPUT TYPE=text NAME="line5" SIZE=12 onChange="compute()"></TD></TR>
<TR> <!-- Line 6: Tax -->
<TD>6.</TD>
<TD>This is your tax, from 1996 tax rate schedules</TD>
<TD><INPUT TYPE=text NAME="tax" SIZE=12 onChange="compute()"></TD></TR>
</TABLE>
<FORM>
</BODY>
| file: /Techref/language/java/SCRIPT/definitive/examples/1.3.txt, 7KB, , updated: 1997/4/4 10:59, local time: 2024/12/3 00:54,
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