new dataset Module and Test

modules/dataset.js

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+function updateDataset(oldVnode, vnode) {
+	var elm = vnode.elm,
+		oldDataset = oldVnode.data.dataset || {},
+		dataset = vnode.data.dataset || {},
+		key
+
+	for (key in oldDataset) {
+		if (!dataset[key]) {
+			delete elm.dataset[key];
+		}
+	}
+	for (key in dataset) {
+		if (oldDataset[key] !== dataset[key]) {
+			elm.dataset[key] = dataset[key];
+		}
+	}
+}
+
+module.exports = {create: updateDataset, update: updateDataset}

test/dataset.js

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+var assert = require('assert');
+var fakeRaf = require('fake-raf');
+
+var snabbdom = require('../snabbdom');
+fakeRaf.use();
+var patch = snabbdom.init([
+	require('../modules/dataset'),
+]);
+var h = require('../h');
+
+describe('dataset', function() {
+	var elm, vnode0;
+	beforeEach(function() {
+		elm = document.createElement('div');
+		vnode0 = elm;
+	});
+	it('is set on initial element creation', function() {
+		elm = patch(vnode0, h('div', {dataset: {foo: 'foo'}})).elm;
+		assert.equal(elm.dataset.foo, 'foo');
+	});
+	it('updates dataset', function() {
+		var vnode1 = h('i', {dataset: {foo: 'foo', bar: 'bar'}});
+		var vnode2 = h('i', {dataset: {baz: 'baz'}});
+		elm = patch(vnode0, vnode1).elm;
+		assert.equal(elm.dataset.foo, 'foo');
+		assert.equal(elm.dataset.bar, 'bar');
+		elm = patch(vnode1, vnode2).elm;
+		assert.equal(elm.dataset.baz, 'baz');
+		assert.equal(elm.dataset.foo, undefined);
+	});
+	it('handles string conversions', function() {
+		var vnode1 = h('i', {dataset: {dash: '-', dashed:'a-b', camel: 'aB', integer:0, float:0.1}});
+		elm = patch(vnode0, vnode1).elm;
+
+		assert.equal(elm.dataset.dash, '-');
+		assert.equal(elm.dataset.dashed, 'aB');
+		assert.equal(elm.dataset.camel, 'aB');
+		assert.equal(elm.dataset.integer, '0');
+		assert.equal(elm.dataset.float, '0.1');
+	});
+
+});
+
+fakeRaf.restore();