allow children to be string objects

fixes #977

src/h.ts

@@ -26,11 +26,11 @@ export function h(sel: any, b?: any, c?: any): VNode {
   if (c !== undefined) {
     if (b !== null) { data = b; }
     if (is.array(c)) { children = c; }
-    else if (is.primitive(c)) { text = c; }
+    else if (is.primitive(c)) { text = c.toString(); }
     else if (c && c.sel) { children = [c]; }
   } else if (b !== undefined && b !== null) {
     if (is.array(b)) { children = b; }
-    else if (is.primitive(b)) { text = b; }
+    else if (is.primitive(b)) { text = b.toString(); }
     else if (b && b.sel) { children = [b]; }
     else { data = b; }
   }

src/is.ts

@@ -1,4 +1,4 @@
 export const array = Array.isArray;
 export function primitive(s: any): s is (string | number) {
-  return typeof s === 'string' || typeof s === 'number';
+  return typeof s === 'string' || typeof s === 'number' || s instanceof String;
 }

test/core.js

@@ -67,6 +67,18 @@ describe('snabbdom', function() {
       var vnode = h('a', {}, 'I am a string');
       assert.equal(vnode.text, 'I am a string');
     });
+    it('can create vnode with String obj content', function() {
+      var vnode = h('a', new String('b'));
+      assert.equal(vnode.text, 'b');
+    });
+    it('can create vnode with props and String obj content', function() {
+      var vnode = h('a', {}, new String('b'));
+      assert.equal(vnode.text, 'b');
+    });
+    it('can create vnode with array String obj content', function() {
+      var vnode = h('a', ['b', new String('c')]);
+      assert.equal(vnode.text, 'bc');
+    });
     it('can create vnode with null props', function() {
       var vnode = h('a', null);
       assert.deepStrictEqual(vnode.data, {});