student loan calculator

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
var owe="hello!";
var loan=0;
var loaninterest=0;
var loaninterestrate;
var salary=[0,0,0,14881,16955,19076,21542,23375,25440,26182,27324,29448,30308,31391,31384,32510,32532,33335,33960,33712,33907,35169,35401,35467,35444,35401,35040,35677,35225,35297,36279,35357,36034,36082,34870,35386,35922,35267,34337,33402,32770,32257,29292,28207,27139,23858,24458];
var newsalary={};
var repayments=0
var salarygrowthrate=5.1;
var tuitionfees=9250;
var maintenanceloan=7000;
var lengthofcourse=3;
var owe={};

var svg = d3.select("body").append("svg")
      .attr("width", 960)
      .attr("height", 2000)    
    
    
for (var i = 0; i < 30; i++) {
//increase the loan while studying
  if(i<lengthofcourse){loan=loan+tuitionfees+maintenanceloan}

// increase the salary with a growth rate  
  newsalary[i]=salary[i]*Math.pow((100+salarygrowthrate)/100,i)
  console.log(salary[i],newsalary[i])
  //set the interest rate dependant on salary

if(newsalary[i]<21000){loaninterestrate=3.1;}else if(newsalary[i]>21000&&newsalary[i]<41000){loaninterestrate=3.1+((newsalary[i]-21000)/20000)*3.0}else if(newsalary[i]>41000){loaninterestrate=6.1};
  
  // while studying, interest rate is 6.1%  
if(i<3){loaninterestrate=6.1}
  
  //calculate the interest
loaninterest=loan*(loaninterestrate/100)
//console.log(loaninterest)
//add in the interest to the loan
loan=loan+loaninterest
//console.log(loaninterestrate)
	//calculate the repayments
if(newsalary[i]>21000){repayments=(newsalary[i]-21000)*0.09}

//calculate how much you owe
loan=loan-repayments

console.log(loan,newsalary[i], loaninterest,loaninterestrate,repayments)
owe[i]=loan;

svg.append("text")
      .text(loan)
      .attr("y", 20+20*i)
      .attr("x", 120)
      .attr("font-size", 12)
      .attr("font-family", "monospace")
    
    svg.append("text")
      .text(i)
      .attr("y", 20+20*i)
      .attr("x", 60)
      .attr("font-size", 12)
      .attr("font-family", "monospace")
    	
}
console.log(owe)

</script>
</body>

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