index.js

const colors = require('color-name-list')

function stringToHex (hex) {
  // Convert to string and make sure input color is in Uppercase
  hex = (hex || '000000').toString().toUpperCase()
  // Check if the hex code starts with #, If not then prepend a # to the code.
  hex = (hex.substring(0, 1) === '#') ? hex : `#${hex}`
  // Check if the input code is a valid hex, if not return black #000
  const isHex = /^#([0-9a-f]{3}|[0-9a-f]{6})$/i.test(hex)
  hex = isHex ? hex : '#000000'
  // Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
  const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i
  hex = hex.replace(shorthandRegex, (m, r, g, b) => `${r}${r}${g}${g}${b}${b}`)
  return hex
}

function hexToRGB (hex) {
  // Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
  const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i
  hex = hex.replace(shorthandRegex, (m, r, g, b) => `${r}${r}${g}${g}${b}${b}`)

  const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)

  return result
    ? {
        R: parseInt(result[1], 16),
        G: parseInt(result[2], 16),
        B: parseInt(result[3], 16)
      }
    : {}
}

/*
  http://www.easyrgb.com/en/math.php
  (Standard RGB) input range = 0 ÷ 255
  X, Y and Z output refer to a D65/2° standard illuminant.
*/

function rgbToXYZ (RGB) {
  const RED = ((RGB.R / 255) > 0.04045) ? Math.pow((((RGB.R / 255) + 0.055) / 1.055), 2.4) * 100 : ((RGB.R / 255) / 12.92) * 100
  const GREEN = ((RGB.G / 255) > 0.04045) ? Math.pow((((RGB.G / 255) + 0.055) / 1.055), 2.4) * 100 : ((RGB.G / 255) / 12.92) * 100
  const BLUE = ((RGB.B / 255) > 0.04045) ? Math.pow((((RGB.B / 255) + 0.055) / 1.055), 2.4) * 100 : ((RGB.B / 255) / 12.92) * 100

  const Xv = (RED * 0.4124) + (GREEN * 0.3576) + (BLUE * 0.1805)
  const Yv = (RED * 0.2126) + (GREEN * 0.7152) + (BLUE * 0.0722)
  const Zv = (RED * 0.0193) + (GREEN * 0.1192) + (BLUE * 0.9505)

  return {
    X: Xv,
    Y: Yv,
    Z: Zv
  }
}

/*
  http://www.easyrgb.com/en/math.php
  XYZ (Tristimulus) Reference values of a perfect reflecting diffuser
  D65 is illuminants and observer has been choosen
  2° (CIE 1964) REFERENCE_X, REFERENCE_Y and REFERENCE_Z.
  Daylight, sRGB, Adobe-RGB
*/

function xyzToCIELab (XYZ) {
  const REFERENCE_X = 95.047
  const REFERENCE_Y = 100.000
  const REFERENCE_Z = 108.883

  const X = ((XYZ.X / REFERENCE_X) > 0.008856) ? Math.pow((XYZ.X / REFERENCE_X), (1 / 3)) : ((7.787 * (XYZ.X / REFERENCE_X)) + (16 / 116))
  const Y = ((XYZ.Y / REFERENCE_Y) > 0.008856) ? Math.pow((XYZ.Y / REFERENCE_Y), (1 / 3)) : ((7.787 * (XYZ.Y / REFERENCE_Y)) + (16 / 116))
  const Z = ((XYZ.Z / REFERENCE_Z) > 0.008856) ? Math.pow((XYZ.Z / REFERENCE_Z), (1 / 3)) : ((7.787 * (XYZ.Z / REFERENCE_Z)) + (16 / 116))

  const CIEL = (116 * Y) - 16
  const CIEA = 500 * (X - Y)
  const CIEB = 200 * (Y - Z)

  return {
    L: CIEL,
    a: CIEA,
    b: CIEB
  }
}

function rgbToCIELab (RGB) {
  const XYZ = rgbToXYZ(RGB)
  return xyzToCIELab(XYZ)
}

/*
  http://www.easyrgb.com/en/math.php
  https://en.wikipedia.org/wiki/Color_difference

  Delta E* CIE return value table
  http://zschuessler.github.io/DeltaE/learn/#toc-defining-delta-e
*/

function deltaE1994 (CIELab1, CIELab2) {
  const DeltaE94 = Math.sqrt(Math.pow((CIELab1.L - CIELab2.L), 2) + Math.pow((CIELab1.a - CIELab2.a), 2) + Math.pow((CIELab1.b - CIELab2.b), 2))
  return DeltaE94
}

/*
  Delta E Perception
  <= 1.0 Not perceptible by human eyes.
  1 - 2 Perceptible through close observation.
  2 - 10 Perceptible at a glance.
  11 - 49 Colors are more similar than opposite
  100 Colors are exact opposite
  status
  0 Exact Match
  2 Not perceptible by human eyes.
  4 Perceptible through close observation.
  8 Perceptible at a glance.
  16 Colors are exact opposite
*/

function matchColor (CIELab1, ColorCollection) {
  const delta = deltaE1994(CIELab1, ColorCollection.cieLab)
  if (delta === 0) {
    return {
      status: 1,
      name: ColorCollection.name,
      hex: ColorCollection.hex,
      delta,
      message: 'Exact Match'
    }
  } else if (delta > 0 && delta <= 1) {
    return {
      status: 2,
      name: ColorCollection.name,
      hex: ColorCollection.hex,
      delta,
      message: 'Not perceptible by human eyes'
    }
  } else if (delta > 1 && delta < 2) {
    return {
      status: 4,
      name: ColorCollection.name,
      hex: ColorCollection.hex,
      delta,
      message: 'Perceptible through close observation'
    }
  } else if (delta >= 2 && delta < 10) {
    return {
      status: 8,
      name: ColorCollection.name,
      hex: ColorCollection.hex,
      delta,
      message: 'Perceptible at a glance'
    }
  }
  return {
    status: -1,
    delta,
    message: 'No Color match found'
  }
}

module.exports = function (hexcolor) {
  hexcolor = stringToHex(hexcolor)
  const rgbColor = hexToRGB(hexcolor)
  const cieLabColor = rgbToCIELab(rgbColor)
  const matchedColor = []
  colors.forEach(element => {
    const hexValue = stringToHex(element.hex)
    const rgbValue = hexToRGB(hexValue)
    const cieLabValue = rgbToCIELab(rgbValue)
    element.cieLab = cieLabValue
    if (matchColor(cieLabColor, element).status > 0) {
      matchedColor.push(matchColor(cieLabColor, element))
    }
  })

  const matched = matchedColor.reduce((prevColor, currentColor) => (prevColor.delta < currentColor.delta) ? prevColor : currentColor)
  return matched
}