Javascript | Floating point numbers + interval loop

Question

I have a floating point number (for example): 0.004178174922295

How could I get the decremental function to make a calculations from this number to 0 in specific amount of time (for example 1 second)? Thanks.

Expected values:

0.004178174922295
0.004178174922294
0.004178174922293
...
0

Answer 1

As raina77ow and others pointed out in the comments, operations with decimal numbers are problematic in JS, approximations are made and the results may be inexact.

A workaround would be turn the infinitesimals into big integral numbers, work with them and convert them back at the end.

Is this what you were looking for? Please let me know.

EDIT You can ask for the countdown to be done in a certain amount of time, it does work with reasonable numbers, but in Javascript the minimum interval is of 10 milliseconds, you can't call intervals shorter than that. With the example number you gave, 0.004178174922295, it's like counting down from 4178174922295 to zero. That would requiere almost 1325 years in 10 millisecond intervals (if my math is correct, either way I expect you were going to pass a much shorter lapse).

function infinitesimalCountDown(num, seconds) {
  // I create a coeficient to convert the decimal to an int
  // Will be a big number starting with "1" and followed by a bunch of zeroes
  let coefString = '1';
  for(let i=0; i<num.toString().length-2; i++) {
    coefString += '0';
  }

  const coef = Number(coefString);

  // This has the digits from the original original but it's an int
  let counter = Math.round(num*coef);

  // Now I can just treat it as an int and convert it back for the output
  const icdInterval = setInterval(() => {
    counter--;
    console.log(counter/coef);
    if(counter <= 0) clearInterval(icdInterval);
  }, Math.round(seconds*1000/counter));
}

console.log("It works with a short number");

infinitesimalCountDown(0.0041, 10);

setTimeout(() => {
  console.log("It doesn't work with a long number");
  infinitesimalCountDown(0.004178174922295, 3000);
}, 12 * 1000);

If you are fine with the steps being the necessary for Javascript to be able to process it, you can do the following:

function infinitesimalCountDown(num, seconds) {
  let coefString = '1'
  
  for(let i=0; i<num.toString().length-2; i++) {
    coefString += '0'
  }

  const coef = Number(coefString)
  
  let counter = Math.round(num*coef)
  
  let steps = seconds * 1000 / counter
  
  steps = steps < 100 ? 100 : steps
  
  let step = 1
  
  if(steps == 100) {
    step = counter / ((seconds * 1000) / steps)
  }
  
  console.log(step)
  
  const icdInterval = setInterval(() => {
    counter -= step;
    if(counter <= 0) {
      counter = 0
      clearInterval(icdInterval)
    }
    console.log(counter/coef)
  }, steps)
}

infinitesimalCountDown(0.004178174922295, 5)