There a lot of problems, I am afraid. Not least that you are using the same name for an HTML element and a Javascript variable, and, worse, you are using the same name
BodyFat both as the name of a function and the name of a variable.
The concat() method is used to join two or more
arrays.
You have left out the <body> and </body> tags.
And nowhere do you actually calculate the Body Fat Index.
But I give you credit for correctly using the radix 10 with parseInt() - although Number() would have been just as good and would give you the opportunity to trap NaN entries, thus:-
var weight = Number(document.getElementById("weightBox").value) || 0 ; // return 0 if not a number
I have put it right for you following the guidance in your first post.
Please study and learn from it!
Code:
<html>
<head>
<title> BodyFat Formula </title>
<script type="text/javascript">
function BodyFat() {
var weight = parseInt(document.getElementById("weightBox").value, 10);
var waist = parseInt(document.getElementById("waistBox").value, 10);
var Factor1 = weight * 1.082 + 94.42;
var Factor2 = waist * 4.15;
var LBMass = Factor1 - Factor2;
var BFWeight = weight - LBMass;
var BFPercent = (BFWeight * 100/ weight).toFixed(2); // 2 decimal places
document.getElementById("bodyfatBox").value = BFPercent;
}
</script>
</head>
<body>
<h2>BodyFat Formula</h2>
Weight: <input type="text" id="weightBox" size="4" value="150"> pounds
<br>
Waist measurement: <input type="text" id="waistBox" size="4" value="32" > inches
<br>
BodyFat: <input type="text" id="bodyfatBox" size=4 value=0> percent
<br>
<input type="button" value="Calculate body fat" onclick="BodyFat();">
<hr>
</body>
</html>
It is not really in your best interests that others do your all or most homework for you. Your teacher may gain a false and exaggerated idea of your programming capabilities and so not offer you the support you need. Also, if you hand in other people's work which you do not completely understand, then you will start to fall behind and your difficulties will increase.
I am happy to give you a push forward, but remember that there is a limit to the number of times that you can take your pitcher to this well!
I also endorse the comments of Logic Ali regarding the use of the error console.