从网上看了个案例，是实现颜色值转换的，就想着自己也写个。网上的案例链接找不到了，这里也就不贴了。

JavaScript颜色转换的核心就是进制间的转换。

rgba(0,0,0,.4)转换成#000000，就是Number.toString(16)

#ffffff转换成rgb(255,255,255)，就是parseInt(String,16)

 

代码如下：

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" Content="text/html; charset=utf-8;">
<title>JS-颜色值的转换</title>
<meta name="author" content="rainna" />
<meta name="keywords" content="rainna's js lib" />
<meta name="description" content="js" />
<style>
*{margin:0;padding:0;}
body{background:#f0f0f0;}
h2{margin:0 0 20px;}
input{width:300px;height:24px;line-height:24px;}

.m-box{width:900px;margin:0 auto;padding:20px;}
</style>
</head>

<body>
<div class="m-box">
    <h2>RGB(A)颜色转换为HEX十六进制的颜色值</h2>
    <div class="box1">
        <input type="text" id="colorIpt1" value="rgba(0,0,0,.4)"/>
        <a href="#" id="link1">转换</a>
        <input type="text" id="colorIpt2"/>
    </div>
</div>

<div class="m-box">
    <div class="box1">
        <input type="text" id="colorIpt3" value="#ffffff"/>
        <a href="#" id="link2">转换</a>
        <input type="text" id="colorIpt4"/>
    </div>
</div>

<script>
var colorChange = {
    rgbToHex:function(val){  //RGB(A)颜色转换为HEX十六进制的颜色值
        var r, g, b, a,
        regRgba = /rgba?\((\d{1,3}),(\d{1,3}),(\d{1,3})(,([.\d]+))?\)/,    //判断rgb颜色值格式的正则表达式，如rgba(255,20,10,.54)
        rsa = val.replace(/\s+/g,'').match(regRgba);
        if(!!rsa){
            r = parseInt(rsa[1]).toString(16);
            r = r.length == 1 ? '0' + r : r;
            g = (+rsa[2]).toString(16);
            g = g.length == 1 ? '0' + g : g;
            b = (+rsa[3]).toString(16);
            b = b.length == 1 ? '0' + b : b;
            a = (+(rsa[5] ? rsa[5] : 1)) * 100;
            return {hex:'#' + r + g + b, alpha: Math.ceil(a)};
        }else{
            return {hex:val, alpha:100};
        }    
    },
    hexToRgb:function(val){   //HEX十六进制颜色值转换为RGB(A)颜色值
        var a,b,c;
        if((/^#/g).test(val)){
            a = val.slice(1,3);
            b = val.slice(3,5);
            c = val.slice(5,7);
            return {rgba:'rgb(' + parseInt(a,16) + ',' + parseInt(b,16) + ',' + parseInt(c,16) + ')'};
        }else{
            return {rgba:'无效值：' + val};
        }
    }
};

link1.onclick = function(){
    var obj = colorChange.rgbToHex(document.getElementById('colorIpt1').value);
    document.getElementById('colorIpt2').value = '颜色值：' + obj.hex + '，透明度：' + obj.alpha + '%';
};
link2.onclick = function(){
    var obj = colorChange.hexToRgb(document.getElementById('colorIpt3').value);
    document.getElementById('colorIpt4').value = '颜色值：' + obj.rgba;
};
</script>
</body>
</html>