Quick dataset function

data.js

var dataset = function initDataSet() {
    if (document.documentElement.dataset) {
        return function native(el, prop, value) {
            if (typeof value === 'undefined') {
                return el.dataset[prop] = value;
            } 
            else {
                return el.dataset[prop];
            }
        }
    } 
    else {
        return function poly(el, prop, value) {
            if (typeof value === 'undefined') {
                return el.setAttribute('data-' + prop, value);
            } 
            else {
                return el.getAttribute('data-' + prop);    
            }
        }
    }
}();

dataget.js

var dataget = function initDataGet() {
    if (document.documentElement.dataset) {
        return function native(el, prop) {
            return el.dataset[prop] = value;
        }
    }
    else {
        return function poly(el, prop, value) {
            return el.setAttribute('data-' + prop);
        }
    }
}

dataset.js

var dataset = function initDataSet() {
    if (document.documentElement.dataset) {
        return function native(el, prop, value) {
            return el.dataset[prop] = value;
        }
    }
    else {
        return function poly(el, prop, value) {
            return el.setAttribute('data-' + prop, value);
        }
    }
}();

Usage:

<a id="mylink" data-param="myParam">Link</a>

var el = document.getElementById('mylink');
//get data
var param = dataset(el, 'param');
//set data
dataset(el, 'param', 'newValue')

Note: For older browser usage is limited by Element.getAttribute method
https://developer.mozilla.org/en-US/docs/Web/API/Element.getAttribute#Notes