JSFiddle - React, Tailwind, and code Playground

by grant

HTML

<div id="total"></div>
<div id="rooster"></div>
<div id="hen"></div>
<div>
<a href="https://stackoverflow.com/questions/23759782/javascript-percentage-difference-between-two-values" target="_blank">% diff StackO</a>
</div>
<div>
<a href="https://stackoverflow.com/questions/30922008/calculate-percentage-javascript" target="_blank">percentage S O</a>
</div>

JavaScript

/*
Step 1: Calculate the change (subtract old value from the new value)
Step 2: Divide that change by the old value (you will get a decimal number)
Step 3: Convert that to a percentage (by multiplying by 100 and adding a "%" sign)
*/


function perc(oldValue, newValue) {
   return ((newValue / oldValue) * 100).toFixed(0)+"%"
}
console.log(perc(100, 50))

function relDiff(a, b) {
 return  100 * Math.abs( ( a - b ) / ( (a+b)/2 ) ).toFixed(2)+"%";
}
var data =[
 {"year":2020,"total":72,"Rooster":21,"Hen":30,"Quail":26},
 {"year":2021,"total":28,"Rooster":1,"Hen":15,"Quail":2}
]

for (let i = 0; i < data.length; i++) {
  total = ((((data[i+1].total) / (data[i].total))* 100).toFixed(2)+"% total")
  rooster = ((((data[i+1].Rooster) / (data[i].Rooster))* 100).toFixed(2)+"% rooster")
  hen = ((((data[i+1].Hen) / (data[i].Hen))* 100).toFixed(2)+"% hen")
  console.log(two = (data[i+1].Hen))
 console.log(one = (data[i].Hen))
  
 // console.log(rooster)
diff = relDiff( one, two )
  console.log(diff+" difference")
 
  break; 
  
  }
var employees = [
    {name: "Tony Stark", department: "IT"},
    {name: "Peter Parker", department: "Pizza Delivery"},
    {name: "Bruce Wayne", department: "IT"},
    {name: "Clark Kent", department: "Editing"}
];
var chickens = [
  {year:2020, total:72, Rooster:21, Hen:30, Quail:26}, 
 {year:2021, total:28, Rooster:1, Hen:15, Quail:2}
]
  
var output =  chickens.filter(employee => employee.Hen >= 0);
//var output =  employees.filter(employee => employee.department == "IT");
console.log(output)
for(var i=0;i<output.length;i++){
   document.write("<div>", output[i].year, " - ", output[i].Hen, "</div>")
}
  document.getElementById("total").innerHTML = total
  document.getElementById("rooster").innerHTML = rooster
  document.getElementById("hen").innerHTML = hen