The visibility of these fields is controlled from a enableElements-function:

[percentage, units, volume].forEach(el => el.disabled = !bool);

When we then add the beverage, a list of consumed beverages is created, and the BAC, estimated hours to sober up, etc., are calculated:

You can then continue to add more beverages, and the BAC updates accordingly:

It was very surprising for me to learn, that the legal BAC in the U.S. is 4x greater than that of Sweden or Norway!

In other words, in Sweden, you could lose your license for drinking an amount that would be legally permissible in the U.S.

Breaking Down the BAC Calculation

The core calculation for BAC is handled in the calculateAnswer function:

function calculateAnswer() {
  const alcoholMetabolismRate = 0.015;
  const currentBAC =
    ((total * 10) /
      (weight.valueAsNumber *
        1000 *
        parseFloat(bodywater.value))) *
    100;
  const hoursToSober = (
    currentBAC / alcoholMetabolismRate
  ).toFixed(1);
  const canDrive =
    currentBAC 



Let’s break it down:


Alcohol Metabolism Rate: alcoholMetabolismRate = 0.015

This value represents the average rate at which the body reduces BAC per hour (approximately 0.015%).


Calculating Current BAC: currentBAC = ((total * 10) / ((weight.valueAsNumber * 1000) * parseFloat(bodywater.value))) * 100


total * 10: This converts the total alcohol units consumed into grams (since one unit equals about 10 grams of pure alcohol).

weight.valueAsNumber * 1000: Converts body weight from kilograms to grams for calculation purposes.

bodywater.value: A decimal factor based on biological gender, affecting how alcohol distributes in the body (e.g., 0.58 for males, 0.49 for females).
The result is then multiplied by 100 to convert BAC to a percentage.


Estimating Hours to Sober: hoursToSober = (currentBAC / alcoholMetabolismRate).toFixed(1);

Divides the currentBAC by the metabolism rate to estimate the time needed for BAC to reach zero.


Determining Legal Driving Status: canDrive = currentBAC 

Compares currentBAC to the selected legal BAC limit. If the current BAC is within the limit, the user is considered "fit to drive"; otherwise, they are not.

The calculateAnswer function then combines these values into a message that shows the current BAC, hours until sober, and whether the user is fit to drive.


… And that concludes this tutorial. Feel free to experiment with the CodePen if you’d like — perhaps by creating a more child-friendly UX. Just remember, this tool provides an estimate and doesn’t account for factors like the time you consumed each beverage. And keep in mind, it will most likely be used by sober people!



  
  
  Demo






Cover by DALL·E, from the prompt: Generate a drunk car in a cartoonish style similar to early Disney and Cupheads, as an image I can crop to 1000x420px.