Added function to wait until element appears in DOM

src/util/waitForElement.js

@@ -0,0 +1,62 @@
+/**
+ * Waits until Element will appear
+ * @param {HTMLElement} elSelector Selector to locate Element
+ * @param {number} timeout Maximum timeout after which Error will be thrown
+ * @param {() => void} callback Callback to be called after Element appearance
+ */
+export default function waitForElement(elSelector, callback) {
+  if (document.querySelector(elSelector) !== null) {
+    callback();
+    return;
+  }
+
+  if (typeof MutationObserver !== "undefined") {
+    /* jshint ignore:start */
+    const observer = new MutationObserver(() => {
+      if (document.querySelector(elSelector) !== null) {
+        observer.disconnect();
+        callback();
+      }
+    });
+    /* jshint ignore:end */
+
+    observer.observe(document.body, {
+      childList: true,
+      subtree: true,
+      attributes: false,
+      characterData: false,
+    });
+  } else {
+    // Old browsers will wait by timeout
+    waitForElementByTimeout(elSelector, callback, 1000, 10000);
+  }
+}
+
+/**
+ * @param {string} elSelector
+ * @param {() => void} callback
+ * @param {number} checkInterval In milliseconds
+ * @param {number} maxTimeout In milliseconds
+ */
+function waitForElementByTimeout(
+  elSelector,
+  callback,
+  checkInterval,
+  maxTimeout
+) {
+  let startTimeInMs = Date.now();
+  (function loopSearch() {
+    if (document.querySelector(elSelector) !== null) {
+      callback();
+      return;
+    } else {
+      setTimeout(function () {
+        if (Date.now() - startTimeInMs > maxTimeout) {
+          callback();
+          return;
+        }
+        loopSearch();
+      }, checkInterval);
+    }
+  })();
+}