SOURCE

var util = {
    cutHex: function (hex) {
        return hex.charAt(0) == "#" ? hex.substring(1, 7) : hex;
    },
    hexToR: function (hex) {
        return parseInt((util.cutHex(hex)).substring(0, 2), 16)
    },
    hexToG: function (hex) {
        return parseInt((util.cutHex(hex)).substring(2, 4), 16)
    },
    hexToB: function (hex) {
        return parseInt((util.cutHex(hex)).substring(4, 6), 16)
    },
    hexToRgba: function (hex) {
        return 'rgba('+util.hexToR(hex)+','+util.hexToG(hex)+','+util.hexToB(hex)+',0.1)';
    }
};

function showRGB2(){
   var hex= document.getElementsByName("rgb2")[0].value;

   console.log(hex);
  var rgba= util.hexToRgba(hex);
  console.log(rgba);

  document.getElementById("rgba").innerHTML=rgba+';'
  
}

<div>十六进制颜色码转换成RGBA颜色值：</div>

<input name="rgb2" value="393d499e" size="8" maxlength="9" >
<input onclick="showRGB2()" type="button" value="转换" name="button">
<div id="rgba">123</div>