refactor: demo ie11 polyfill added

Author: xidedix

demo/src/index.js

@@ -2,6 +2,7 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import App from './App';
 // import registerServiceWorker from './registerServiceWorker';
+import './polyfill'
 
 ReactDOM.render(<App />, document.querySelector('#demo'))
 // ReactDOM.render(<App />, document.getElementById('root'));

demo/src/polyfill.js

@@ -0,0 +1,24 @@
+// IE11 polyfills
+
+if (!Array.prototype.find) {
+  Array.prototype.find = function(predicate) {
+    if (this == null) {
+      throw new TypeError('Array.prototype.find called on null or undefined');
+    }
+    if (typeof predicate !== 'function') {
+      throw new TypeError('predicate must be a function');
+    }
+    const list = Object(this);
+    const length = list.length >>> 0;
+    const thisArg = arguments[1];
+    let value;
+
+    for (let i = 0; i < length; i++) {
+      value = list[i];
+      if (predicate.call(thisArg, value, i, list)) {
+        return value;
+      }
+    }
+    return undefined;
+  };
+}