Dataset Shim

html5-dataset.js

/**
 * Add dataset support to elements
 * No globals, no overriding prototype with non-standard methods, 
 *   handles CamelCase properly, attempts to use standard 
 *   Object.defineProperty() (and Function bind()) methods, 
 *   falls back to native implementation when existing
 * Inspired by http://code.eligrey.com/html5/dataset/ 
 *   (via https://github.com/adalgiso/html5-dataset/blob/master/html5-dataset.js )
 * Depends on Function.bind and Object.defineProperty/Object.getOwnPropertyDescriptor (polyfills below)
 * All code below is Licensed under the X11/MIT License
*/

// Inspired by https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/bind#Compatibility
if (!Function.prototype.bind) {
    Function.prototype.bind = function (oThis) {
        'use strict';
        if (typeof this !== "function") {
            // closest thing possible to the ECMAScript 5 internal IsCallable function
            throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");
        }

        var aArgs = Array.prototype.slice.call(arguments, 1),
            fToBind = this,
            FNOP = function () {},
            fBound = function () {
                return fToBind.apply(
                    this instanceof FNOP && oThis ? this : oThis,
                   aArgs.concat(Array.prototype.slice.call(arguments))
               );
            };

        FNOP.prototype = this.prototype;
        fBound.prototype = new FNOP();

        return fBound;
    };
}

/*
 * Xccessors Standard: Cross-browser ECMAScript 5 accessors
 * http://purl.eligrey.com/github/Xccessors
 * 
 * 2010-06-21
 * 
 * By Eli Grey, http://eligrey.com
 * 
 * A shim that partially implements Object.defineProperty,
 * Object.getOwnPropertyDescriptor, and Object.defineProperties in browsers that have
 * legacy __(define|lookup)[GS]etter__ support.
 * 
 * Licensed under the X11/MIT License
 *   See LICENSE.md
*/

// Removed a few JSLint options as Notepad++ JSLint validator complaining and 
//   made comply with JSLint; also moved 'use strict' inside function
/*jslint white: true, undef: true, plusplus: true,
  bitwise: true, regexp: true, newcap: true, maxlen: 90 */

/*! @source http://purl.eligrey.com/github/Xccessors/blob/master/xccessors-standard.js*/

(function () {
    'use strict';
    var ObjectProto = Object.prototype,
    defineGetter = ObjectProto.__defineGetter__,
    defineSetter = ObjectProto.__defineSetter__,
    lookupGetter = ObjectProto.__lookupGetter__,
    lookupSetter = ObjectProto.__lookupSetter__,
    hasOwnProp = ObjectProto.hasOwnProperty;
    
    if (defineGetter && defineSetter && lookupGetter && lookupSetter) {

        if (!Object.defineProperty) {
            Object.defineProperty = function (obj, prop, descriptor) {
                if (arguments.length < 3) { // all arguments required
                    throw new TypeError("Arguments not optional");
                }
                
                prop += ""; // convert prop to string

                if (hasOwnProp.call(descriptor, "value")) {
                    if (!lookupGetter.call(obj, prop) && !lookupSetter.call(obj, prop)) {
                        // data property defined and no pre-existing accessors
                        obj[prop] = descriptor.value;
                    }

                    if ((hasOwnProp.call(descriptor, "get") ||
                         hasOwnProp.call(descriptor, "set"))) 
                    {
                        // descriptor has a value prop but accessor already exists
                        throw new TypeError("Cannot specify an accessor and a value");
                    }
                }

                // can't switch off these features in ECMAScript 3
                // so throw a TypeError if any are false
                if (!(descriptor.writable && descriptor.enumerable && 
                    descriptor.configurable))
                {
                    throw new TypeError(
                        "This implementation of Object.defineProperty does not support" +
                        " false for configurable, enumerable, or writable."
                    );
                }
                
                if (descriptor.get) {
                    defineGetter.call(obj, prop, descriptor.get);
                }
                if (descriptor.set) {
                    defineSetter.call(obj, prop, descriptor.set);
                }
            
                return obj;
            };
        }

        if (!Object.getOwnPropertyDescriptor) {
            Object.getOwnPropertyDescriptor = function (obj, prop) {
                if (arguments.length < 2) { // all arguments required
                    throw new TypeError("Arguments not optional.");
                }
                
                prop += ""; // convert prop to string

                var descriptor = {
                    configurable: true,
                    enumerable  : true,
                    writable    : true
                },
                getter = lookupGetter.call(obj, prop),
                setter = lookupSetter.call(obj, prop);

                if (!hasOwnProp.call(obj, prop)) {
                    // property doesn't exist or is inherited
                    return descriptor;
                }
                if (!getter && !setter) { // not an accessor so return prop
                    descriptor.value = obj[prop];
                    return descriptor;
                }

                // there is an accessor, remove descriptor.writable;
                // populate descriptor.get and descriptor.set (IE's behavior)
                delete descriptor.writable;
                descriptor.get = descriptor.set = undefined;
                
                if (getter) {
                    descriptor.get = getter;
                }
                if (setter) {
                    descriptor.set = setter;
                }
                
                return descriptor;
            };
        }

        if (!Object.defineProperties) {
            Object.defineProperties = function (obj, props) {
                var prop;
                for (prop in props) {
                    if (hasOwnProp.call(props, prop)) {
                        Object.defineProperty(obj, prop, props[prop]);
                    }
                }
            };
        }
    }
}());

// Begin dataset code

if (!document.documentElement.dataset && 
         // FF is empty while IE gives empty object
        (!Object.getOwnPropertyDescriptor(Element.prototype, 'dataset')  ||
        !Object.getOwnPropertyDescriptor(Element.prototype, 'dataset').get)
    ) {
    var propDescriptor = {
        enumerable: true,
        get: function () {
            'use strict';
            var i, 
                that = this,
                HTML5_DOMStringMap, 
                attrVal, attrName, propName,
                attribute,
                attributes = this.attributes,
                attsLength = attributes.length,
                toUpperCase = function (n0) {
                    return n0.charAt(1).toUpperCase();
                },
                getter = function () {
                    return this;
                },
                setter = function (attrName, value) {
                    return (typeof value !== 'undefined') ? 
                        this.setAttribute(attrName, value) : 
                        this.removeAttribute(attrName);
                };
            try { // Simulate DOMStringMap w/accessor support
                // Test setting accessor on normal object
                ({}).__defineGetter__('test', function () {});
                HTML5_DOMStringMap = {};
            }
            catch (e1) { // Use a DOM object for IE8
                HTML5_DOMStringMap = document.createElement('div');
            }
            for (i = 0; i < attsLength; i++) {
                attribute = attributes[i];
                // Fix: This test really should allow any XML Name without 
                //         colons (and non-uppercase for XHTML)
                if (attribute && attribute.name && 
                    (/^data-\w[\w\-]*$/).test(attribute.name)) {
                    attrVal = attribute.value;
                    attrName = attribute.name;
                    // Change to CamelCase
                    propName = attrName.substr(5).replace(/-./g, toUpperCase);
                    try {
                        Object.defineProperty(HTML5_DOMStringMap, propName, {
                            enumerable: this.enumerable,
                            get: getter.bind(attrVal || ''),
                            set: setter.bind(that, attrName)
                        });
                    }
                    catch (e2) { // if accessors are not working
                        HTML5_DOMStringMap[propName] = attrVal;
                    }
                }
            }
            return HTML5_DOMStringMap;
        }
    };
    try {
        // FF enumerates over element's dataset, but not 
        //   Element.prototype.dataset; IE9 iterates over both
        Object.defineProperty(Element.prototype, 'dataset', propDescriptor);
    } catch (e) {
        propDescriptor.enumerable = false; // IE8 does not allow setting to true
        Object.defineProperty(Element.prototype, 'dataset', propDescriptor);
    }
}

test-dataset.html

<!DOCTYPE html>

<script src="html5-dataset.js"></script>

<h3 id="hd" data-ab-cd="zzz">Test!</h3>

<script>
var h = document.getElementById('hd');

for (var i in h) {
    if (i === 'dataset') {alert('iterated an Element object');}
}
for (var i in Element.prototype) {
    if (i === 'dataset') {alert('iterated the Element prototype');}
}


try {
    alert(h.dataset.abCd)
}catch(e) {alert(e);}

h.dataset.abCd = 'abc';
alert(h.dataset.abCd)
    
</script>

The reference to license.md is from the https://github.com/eligrey/Xccessors portion of the code (with his license at https://github.com/eligrey/Xccessors/blob/master/LICENSE.md ). You should be able to just attach this:

MIT license

Copyright © 2012-2018 Brett Zamir except for Xccessors code which is under the same license terms but is copyright © 2010 Elijah Grey, who also goes by Eli Grey.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.