使用Decimal.js计算两个数字之间的百分比增加/减少百分比的正确方法是什么？

Question

Desired Behaviour

Show percentage increase/decrease of new_value in comparison to old_value , showing negative indicator when there has been a decrease, and 4 decimal places (with trailing zeros if necessary).

Actual Behaviour

Good
If old_value is 38.1200 and new_value is 19.0600 result is -50.0000

Not so good
If old_value is 0.0000 and new_value is 1.0000 result is Infinity (I expect the result to be 100.0000 . Edit : I now realise that there is no such thing as a percentage increase from 0 to anything, per posts like this ).

What I've Tried

 var old_value = new Decimal(0.0000); var new_value = new Decimal(1.0000); var difference = new_value.sub(old_value).dividedBy(old_value).times(100).toFixed(4, 7); // without using Decimal.js, the equation above would be: // (new_value - old_value) / old_value * 100 $(".result").text(difference.toString()); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/decimal.js/7.3.0/decimal.min.js"></script> <p class="result"></p> 

Answer 1

I am assuming the equation is correct, it was just the Infinity result that threw me, so here is solution to "handle" the issue:

 var old_value = "38.1200"; if (old_value === "0.0000") { // show an infinity sign or something $(".result").text("HI!!"); } else { old_value = new Decimal(old_value); var new_value = new Decimal(19.0600); var difference = new_value.sub(old_value).dividedBy(old_value).times(100).toFixed(4, 7); $(".result").text(difference.toString()); } 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/decimal.js/7.3.0/decimal.min.js"></script> <p class="result"></p>