calculate % change in javascript

Question

var current = 12000;
var june = 14600;
var may = 11200;

I want percent change with respect to 'current' month parameter. The output should be in percent and it can add or subtract w.r.t. the current month. How to do this?

Van

Answer 1

Its simple maths:

var res=(current-june)/current*100.0;

Heteromorphic

I think this is backwards. It gives the percentage change of the current value vs. June, rather than the other way around. – Pox

@torazaburo: Agree, if comparing to current, it should be res=(x-curr)/curr, so that when x > curr, then res > 0. – Artimas

Right, it's backwards. However, sometimes you need to do it this way. Especially when comparing financial datas, where last quarter is "current" value. – Whispering

Answer 2

Note that if one of your values is 0 you will get either -100% or Infinity%. This solves that problem:

   function percIncrease(a, b) {
        let percent;
        if(b !== 0) {
            if(a !== 0) {
                percent = (b - a) / a * 100;
            } else {
                percent = b * 100;
            }
        } else {
            percent = - a * 100;            
        }       
        return Math.floor(percent);
    }

Chieftain

This should be the accepted answer as it deals with the edge case scenarios. – Negligent

Why have you got Math.floor in there? – Accrete

@Accrete it's to return the largest integer without any decimals. – Citriculture

percIncrease(100, 0); // -10000 – Trucking

Answer 3

var percentchange = (june - current) / current * 100.0;

If your answer is a negative number then this is a percentage increase else decrease.

Shaft

I tried with this. jsbin.com/vibofaleha/edit?html,js,output. and works perfectly fine.. – Van

Same thing, but I'd prefer to write (june/current - 1) * 100. – Pox

Answer 4

It isn't an easy task to handle specials cases, increase or decrease, rounding, over 100%, etc.

function calcPc(n1,n2){
  return (((n2 - n1) / n1 * 100).toLocaleString('fullwide', {maximumFractionDigits:3}) + "%");
}
   
   
   console.log(
   
     " May: "   , calcPc(11200,12000) ,
     "\nJune:" ,  calcPc(14600,12000)
   
   )

Thither