<pre class="shiki github-dark shaku"><code>const validLengths = [4, 7, 5, 9]const validReg = /^#[\da-f]+$/ifunction hexToRgba(hex: string): string { if (!validLengths.includes(hex.length) || !validReg.test(hex)) { throw new Error('invalid hex') } const fullHex = padding(hex) const [r, g, b, a] = parseHex(fullHex) return `rgba(${r},${g},${b},${a})`}function padding(hex: string) { const numberic = hex.slice(1).toLowerCase() if (hex.length === 9) { return numberic } if (hex.length === 5) { return replace(numberic) } if (hex.length === 7) { return numberic + 'ff' } return replace(numberic + 'f')}function replace(str: string) { return str.replace(/./g, s =&gt; s + s)}function parseHex(hex: string) { const [ rHex, gHex, bHex, aHex ] = lenBy(hex) return [ parseColor(rHex), parseColor(gHex), parseColor(bHex), parseAlpha(aHex), ]}function lenBy(hex: string, len = 2) { const list: string[] = [] let start = 0 while(start &lt; hex.length) { const end = start + 2 list.push(hex.slice(start, end)) start = end } return list}function parseColor(colorHex: string, max = 255): number { const num = parseInt(colorHex, 16) if (num &gt; max) { return max } return num}function parseAlpha(alphaHex: string, max = 255): number { const num = parseColor(alphaHex, max) return Math.round(num * 100 / max) / 100}console.log(hexToRgba('#fff'), 'rgba(255,255,255,1)')</code></pre>

easy

Suppose you write some CSS code, you need to set colors. You can choose hexadecimal notation #fff or Functional notation rgba(255,255,255,1). Can you …