fix: handle falsy values correctly in the dataset and style modules (#1094)

ISSUES CLOSED: #303, #1093

src/modules/dataset.ts

@@ -18,7 +18,7 @@ function updateDataset(oldVnode: VNode, vnode: VNode): void {
   const d = elm.dataset;
 
   for (key in oldDataset) {
-    if (!dataset[key]) {
+    if (!(key in dataset)) {
       if (d) {
         if (key in d) {
           delete d[key];

src/modules/style.ts

@@ -42,7 +42,7 @@ function updateStyle(oldVnode: VNode, vnode: VNode): void {
   const oldHasDel = "delayed" in oldStyle;
 
   for (name in oldStyle) {
-    if (!style[name]) {
+    if (!(name in style)) {
       if (name[0] === "-" && name[1] === "-") {
         (elm as any).style.removeProperty(name);
       } else {

test/unit/dataset.ts

@@ -40,6 +40,14 @@ describe("dataset", function () {
     assert.strictEqual(elm.dataset.baz, "baz");
     assert.strictEqual(elm.dataset.foo, undefined);
   });
+  it("handles falsy values", function () {
+    const vnode1 = h("i", { dataset: { foo: "" } });
+    const vnode2 = h("i", { dataset: { foo: "" } });
+    elm = patch(vnode0, vnode1).elm;
+    assert.strictEqual(elm.dataset.foo, "");
+    elm = patch(vnode1, vnode2).elm;
+    assert.strictEqual(elm.dataset.foo, "");
+  });
   it("can be memoized", function () {
     const cachedDataset = { foo: "foo", bar: "bar" };
     const vnode1 = h("i", { dataset: cachedDataset });

test/unit/style.ts

@@ -55,6 +55,14 @@ describe("style", function () {
     patch(vnode2, vnode3);
     assert.strictEqual(elm.style.fontSize, "10px");
   });
+  it("handles falsy values", function () {
+    const vnode1 = h("i", { style: { flexShrink: 0 as any } });
+    const vnode2 = h("i", { style: { flexShrink: 0 as any } });
+    elm = patch(vnode0, vnode1).elm;
+    assert.strictEqual(elm.style.flexShrink, "0");
+    patch(vnode1, vnode2);
+    assert.strictEqual(elm.style.flexShrink, "0");
+  });
   it("implicially removes styles from element", function () {
     const vnode1 = h("div", [h("i", { style: { fontSize: "14px" } })]);
     const vnode2 = h("div", [h("i")]);