feat: add <WhenIdle> component

src/WhenIdle/index.ts

@@ -0,0 +1,39 @@
+import {Component} from 'react';
+
+const RIC = (window as any).requestIdleCallback || ((fn, {timeout = 35} = {}) => setTimeout(fn, 35));
+
+export interface IWhenIdleProps {
+  timeout?: number;
+}
+
+export interface IWhenIdleState {
+  ready: boolean;
+}
+
+export class WhenIdle extends Component<IWhenIdleProps, IWhenIdleState> {
+  mounted = false;
+
+  state: IWhenIdleState = {
+    ready: false
+  };
+
+  componentDidMount () {
+    this.mounted = true;
+
+    const {timeout} = this.props;
+
+    RIC(() => {
+      if (this.mounted) {
+        this.setState({ready: true});
+      }
+    }, {timeout});
+  }
+
+  componentWillUnmount () {
+    this.mounted = false;
+  }
+
+  render () {
+    return this.state.ready ? this.props.children : null;
+  }
+}