Sass color mixing for TypeScript.

README.md

Sass color mixing for TypeScript.

A literal clone of the mixcolor function provided in libsass in TypeScript. Calling the mix function will do the mixing as well as color hex value sanity checking among other things.

color.ts

const clamp = (n: number, min: number, max: number) =>
  n <= min ? min : n >= max ? max : n

const toHex = (v: number) => {
  const h = v.toString(16)
  switch (h.length) {
    case 1:
      return `0${h}`
    case 2:
      return h
    default:
      throw new Error(`expected value from 0~255, got: ${v}`)
  }
}

export class Color extends String {
  constructor(s: string) {
    if (/^#[0-9A-Fa-f]{8}$/.test(s) || /^#[0-9A-Fa-f]{6}$/.test(s)) {
      super(s)
      return
    }
    if (/^#[0-9A-Fa-f]{4}$/.test(s) || /^#[0-9A-Fa-f]{3}$/.test(s)) {
      super(
        `#${s
          .substr(1)
          .split('')
          .map((c) => `${c}${c}`)
          .join('')}`
      )
      return
    }
    throw new Error(`expected color hex string, got '${s}'`)
  }

  get red() {
    return parseInt(this.substr(1, 2), 16)
  }

  get green() {
    return parseInt(this.substr(3, 2), 16)
  }

  get blue() {
    return parseInt(this.substr(5, 2), 16)
  }

  get alpha() {
    return this.length === 9 ? parseInt(this.substr(7, 2), 16) : 1.0
  }

  get hasAlpha() {
    return this.length === 9
  }

  public static fromRGB(r: number, g: number, b: number) {
    return new Color(`#${toHex(r)}${toHex(g)}${toHex(b)}`)
  }

  public static fromRGBA(r: number, g: number, b: number, a: number) {
    return new Color(`${Color.fromRGB(r, g, b)}${toHex(Math.floor(a * 255))}`)
  }

  mix(color: Color, weight = 50) {
    const p = clamp(weight, 0.0, 100.0) / 100.0
    const w = 2.0 * p - 1.0
    const a = this.alpha - color.alpha
    const w1 = ((w * a === -1.0 ? w : (w + a) / (1.0 + w * a)) + 1.0) / 2.0
    const w2 = 1.0 - w1
    const red = Math.round(this.red * w1 + color.red * w2)
    const green = Math.round(this.green * w1 + color.green * w2)
    const blue = Math.round(this.blue * w1 + color.blue * w2)
    const alpha = this.alpha * p + color.alpha * (1.0 - p)
    return this.hasAlpha || color.hasAlpha || alpha !== 1.0
      ? Color.fromRGBA(red, green, blue, alpha)
      : Color.fromRGB(red, green, blue)
  }
}

export const mix = (color1: string, color2: string, weight = 50) =>
  String(new Color(color1).mix(new Color(color2), weight))