feat: implement first version of viewport()

Author: streamich

src/viewport.ts

@@ -0,0 +1,33 @@
+import {Component} from 'react';
+import {h} from './util';
+import {ViewportSensor} from './ViewportSensor';
+import {loadable} from './loadable';
+
+export const viewport = (params) => {
+  const {Loadable} = params;
+
+  const Viewport = class Viewport extends Component<any, any> {
+    state = {
+      flipped: false
+    };
+
+    onChange = () => {
+      Loadable.load();
+      this.setState({
+        flipped: true
+      });
+    };
+
+    render () {
+      const {flipped} = this.state;
+
+      return flipped ?
+        h(Loadable, this.props) :
+        h(ViewportSensor, {onChange: this.onChange},
+          h('div')
+        );
+    }
+  };
+
+  return Viewport;
+};