const hexToRGB = (hex) => {
if (!/(^\#([a-fA-F0-9]{3})$)|(^\#([a-fA-F0-9]{6})$)/g.test(hex)) return null
let allNumberStr = '0123456789abcdef' // 十六进制的所有数字
let len = hex.slice(1).length;
let str = len === 6 ? hex.slice(1) : hex.slice(1)[0].repeat(2) + hex.slice(1)[1].repeat(2) + hex.slice(1)[2].repeat(2);
let arrStr = str.split('');
let newArrStr = arrStr.map((item, index) => {
return allNumberStr.indexOf((item + '').toLowerCase())
})
let num1 = newArrStr[0] * 16 + newArrStr[1];
let num2 = newArrStr[2] * 16 + newArrStr[3];
let num3 = newArrStr[4] * 16 + newArrStr[5];
return `rgb(${num1}, ${num2}, ${num3})`
}
console.log(hexToRGB('#fffaaa')) //rgb(255, 250, 170)
