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>