calculate % change in javascript

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);
    }

Its simple maths:

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