Forms and Math page 4

A discount may be in many formats, but a percentage of the sales price above a certain figure is the most common. We'll create a stand-alone function that will calculate the discount, a "generic" function that can be used again and again. The function will contain 3 arguments, val, threshold and rate, and it will return the variable discount. We'll express the rate argument as a percentage.
For example: calculateDiscount(this.form.sub.value,150,"5%") Try it!

<script language="JavaScript">
<!--
function calculateDiscount(val,threshold,rate){
  var discount=(val>threshold)? (val-threshold)*parseFloat(rate)/100:0;
  return discount;
} 
// -->
</script>

The above concept is developed further to create this form:

Enter # of widgets @$29.90 each

Price (Remember this value is not used in the calculation. The Price is stored in a hidden field.)

Subtotal(widgets x price)

5% discount on orders over $150.00

Total (Subtotal - discount)

<script language="JavaScript">
<!--
function calculateDiscount(val,threshold,rate){
  var discount=(val>threshold)? (val-threshold)*parseFloat(rate)/100:0;
  return discount;
} 

function calculate(){
  with(document.maths){
	  if(widgets.value<=0){
		  alert("Positive numbers only, please"); return;
	  }
	  if (widgets.value % 1!=0){
		  if(window.confirm("Round up to "+Math.ceil(widgets.value)+"?")) 
			  {
			  widgets.value=Math.ceil(widgets.value);
			  }
		  else{
			  return;
		  }
	  }
	  var Sub=widgets.value*hiddenField.value;
	  var Disc=calculateDiscount(Sub,150,5);
	  discount.value= Disc? to_currency(Disc,"$"):0;
	  subtotal.value =to_currency(Sub,"$");
	  total.value= to_currency(Sub-Disc,"$");
  }
}
// -->
</script>

Then add the following code to the body of your document:

<form name="maths">
<p><input type="text" name="widgets" size="8">Enter # of widgets @$29.90 each </p>
<p><input type="text" name="price" value="$29.90" size="8">Price</p>
<p><input type="text" name="subtotal"	size="8">Subtotal(widgets x price)</p>
<p><input type="text" name="discount" size="8">5% discount on orders over $150.00</p>
<p><input type="text" name="total" value="Total" size="10">Total(Subtotal - discount)</p>
<p><input type="button" name="Button" value="Calculate" onClick="calculate()">
</form