Calculate ‘nice’ graph domain by rounding up number through a base-10 range. (ES6)

roundUpBaseInRange.js

// Round up to nearest base, in base 10. Works for both negative/positive numbers and numbers -1 < n < 1.
// Useful for calculating a sensible/readible graph domain max if you input the max value of your data.
export const roundUpBaseInRange = (n, bases = [1, 2, 4, 5, 6, 8, 10]) => {
  // Store the sign, so we can restore it for the result lateron
  const sign = Math.sign(n)

  // Get modulus (remove sign) for next steps in calculation
  const modulus = Math.abs(n)

  // Calculate base10 exponent (i.e. amount of digits as float instead of integer)
  const exponent = Math.log10(modulus)

  // Floor of the exponent gives the amount of digits offset from
  // a base10 number with exponent of 1 (i.e. a single digit number).
  // NOTE: If exponent is infinite, that means n is either 0 or -0
  const offset = Math.floor(isFinite(exponent) ? exponent : 0)

  // Cast modulus as single digit number by using digit offset determined above
  const base = modulus * Math.pow(10, -offset)

  // Find the single-digit base to round up to
  const newBase = bases.find((roundTo) => roundTo >= base)

  // Restore original digit offset to new base
  const result = newBase * Math.pow(10, offset)

  // Restore original sign and return result
  return sign * result
}