XML-escape given string

annotated.js

function (s) {
    return s.replace(
        /[&<>'"]/g, // All characters we want to escape
        function (c){
            return "&" // prefix
                + { // lookup map
                      "&": "amp",
                      "<": "lt",
                      ">": "gt",
                      "'": "apos",
                      '"': "quot"
                  }[c]
                + ";" // suffix
        })
}

index.js

function(s){return s.replace(/[&<>'"]/g,function(c){return "&"+{"&":"amp","<":"lt",">":"gt","'":"apos",'"':"quot"}[c]+";"})}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 Ates Goral <http://magnetiq.com>

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{
  "name": "xmlEscape",
  "description": "Escape basic XML characters",
  "keywords": [
    "string",
    "escaping",
    "xml" 
  ]
}

test.js

var xmlEscape = function(s){return s.replace(/[&<>'"]/g,function(c){return "&"+{"&":"amp","<":"lt",">":"gt","'":"apos",'"':"quot"}[c]+";"})};

console.log(xmlEscape("testing <element attribute=\"value\"> & apostrophe (')"));
// testing &lt;element attribute=&quot;value&quot;&gt; &amp; apostrophe (&apos;)

I win, 39 byte

s=>new Audio(s).outerHTML.slice(27,-10)

@jimmywarting ES6 FTW!