Add polyfill for padStart function

app/javascript/components/SiteSettings/PostStatuses/PostStatusForm.tsx

@@ -2,6 +2,8 @@ import * as React from 'react';
 
 import Button from '../../shared/Button';
 
+import padStart from '../../../helpers/padStart';
+
 interface Props {
   mode: 'create' | 'update';
 
@@ -47,7 +49,7 @@ class PostStatusForm extends React.Component<Props, State> {
   }
 
   getRandomColor() {
-    return '#' + (Math.random() * 0xFFFFFF << 0).toString(16).padStart(6, '0');
+    return '#' + padStart((Math.random() * 0xFFFFFF << 0).toString(16), 6, '0');
   }
 
   isFormValid() {

app/javascript/helpers/padStart.js

@@ -0,0 +1,20 @@
+// padStart has been introduced in ES2017, but right now we're running on ES2016
+// This is a MDN polyfill used as an alternative
+// TODO: switch to ES2017 and remove this script
+
+function padStart(str, targetLength, padString) {
+  targetLength = targetLength>>0; //truncate if number or convert non-number to 0;
+  padString = String((typeof padString !== 'undefined' ? padString : ' '));
+  if (str.length > targetLength) {
+      return String(str);
+  }
+  else {
+      targetLength = targetLength-str.length;
+      if (targetLength > padString.length) {
+          padString += padString.repeat(targetLength/padString.length); //append to original to ensure we are longer than needed
+      }
+      return padString.slice(0,targetLength) + String(str);
+  }
+};
+
+export default padStart;