var hexDigits = new Array
        ("0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"); 

//Function to convert rgb color to hex format
function rgb2hex(rgb) {
 rgb = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
 return "#" + hex(rgb[1]) + hex(rgb[2]) + hex(rgb[3]);
}

function hex(x) {
  return isNaN(x) ? "00" : hexDigits[(x - x % 16) / 16] + hexDigits[x % 16];
 }

(源)

对于所有函数式编程爱好者，这里有一个有点函数式的方法:)

const getHexColor = (rgbValue) =>
  rgbValue.replace("rgb(", "").replace(")", "").split(",")
    .map(colorValue => (colorValue > 15 ? "0" : "") + colorValue.toString(16))
    .reduce((acc, hexValue) => acc + hexValue, "#")

然后这样使用它:

const testRGB = "rgb(13,23,12)"
getHexColor(testRGB)

可读&& Reg-exp自由(无Reg-exp)

我创建了一个函数，它使用可读的基本函数，没有reg-exp。 该函数接受十六进制、rgb或rgba CSS格式的颜色，并返回十六进制表示。 编辑:有一个错误解析出rgba()格式，固定…

function getHexColor( color ){
    //if color is already in hex, just return it...
    if( color.indexOf('#') != -1 ) return color;
    
    //leave only "R,G,B" :
    color = color
                .replace("rgba", "") //must go BEFORE rgb replace
                .replace("rgb", "")
                .replace("(", "")
                .replace(")", "");
    color = color.split(","); // get Array["R","G","B"]
    
    // 0) add leading #
    // 1) add leading zero, so we get 0XY or 0X
    // 2) append leading zero with parsed out int value of R/G/B
    //    converted to HEX string representation
    // 3) slice out 2 last chars (get last 2 chars) => 
    //    => we get XY from 0XY and 0X stays the same
    return  "#"
            + ( '0' + parseInt(color[0], 10).toString(16) ).slice(-2)
            + ( '0' + parseInt(color[1], 10).toString(16) ).slice(-2)
            + ( '0' + parseInt(color[2], 10).toString(16) ).slice(-2);
}

改进功能“hex”

function hex(x){
    return isNaN(x) ? "00" : hexDigits[x >> 4] + hexDigits[x & 0xf];
    // or option without hexDigits array
    return (x >> 4).toString(16)+(x & 0xf).toString(16);
}

这是我的解决方案，也做touppercase使用一个参数和检查其他可能的空白和在提供的字符串大写。

var a = "rgb(10, 128, 255)";
var b = "rgb( 10, 128, 255)";
var c = "rgb(10, 128, 255 )";
var d = "rgb ( 10, 128, 255 )";
var e = "RGB ( 10, 128, 255 )";
var f = "rgb(10,128,255)";
var g = "rgb(10, 128,)";

var rgbToHex = (function () {
    var rx = /^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i;

    function pad(num) {
        if (num.length === 1) {
            num = "0" + num;
        }

        return num;
    }

    return function (rgb, uppercase) {
        var rxArray = rgb.match(rx),
            hex;

        if (rxArray !== null) {
            hex = pad(parseInt(rxArray[1], 10).toString(16)) + pad(parseInt(rxArray[2], 10).toString(16)) + pad(parseInt(rxArray[3], 10).toString(16));

            if (uppercase === true) {
                hex = hex.toUpperCase();
            }

            return hex;
        }

        return;
    };
}());

console.log(rgbToHex(a));
console.log(rgbToHex(b, true));
console.log(rgbToHex(c));
console.log(rgbToHex(d));
console.log(rgbToHex(e));
console.log(rgbToHex(f));
console.log(rgbToHex(g));

据jsfiddle

jsperf的速度比较

进一步的改进可以是trim() rgb字符串

var rxArray = rgb.trim().match(rx),

我漂亮的非标准解

HTML

<div id="selector" style="background-color:#f5b405"></div>

jQuery

$("#selector").attr("style").replace("background-color:", "");

结果

#f5b405