Add getSanitizeDOMValue to settings API (#5617)

* Add  getSanitizeDOMValue to settings API

For environments that don't well support `export let`.

* Add a test for getSanitizeDOMValue

lib/utils/settings.js

@@ -49,7 +49,7 @@ export const setRootPath = function(path) {
  * `type` indicates where the value is being inserted: one of property, attribute, or text.
  * `node` is the node where the value is being inserted.
  *
- * @type {(function(*,string,string,Node):*)|undefined}
+ * @type {(function(*,string,string,?Node):*)|undefined}
  */
 export let sanitizeDOMValue = window.Polymer && window.Polymer.sanitizeDOMValue || undefined;
 
@@ -57,13 +57,22 @@ export let sanitizeDOMValue = window.Polymer && window.Polymer.sanitizeDOMValue
  * Sets the global sanitizeDOMValue available via this module's exported
  * `sanitizeDOMValue` variable.
  *
- * @param {(function(*,string,string,Node):*)|undefined} newSanitizeDOMValue the global sanitizeDOMValue callback
+ * @param {(function(*,string,string,?Node):*)|undefined} newSanitizeDOMValue the global sanitizeDOMValue callback
  * @return {void}
  */
 export const setSanitizeDOMValue = function(newSanitizeDOMValue) {
   sanitizeDOMValue = newSanitizeDOMValue;
 };
 
+/**
+ * Gets sanitizeDOMValue, for environments that don't well support `export let`.
+ *
+ * @return {(function(*,string,string,?Node):*)|undefined} sanitizeDOMValue
+ */
+export const getSanitizeDOMValue = function() {
+  return sanitizeDOMValue;
+};
+
 /**
  * Globally settable property to make Polymer Gestures use passive TouchEvent listeners when recognizing gestures.
  * When set to `true`, gestures made from touch will not be able to prevent scrolling, allowing for smoother

test/unit/property-effects.html

@@ -26,7 +26,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 <script type="module">
 import './property-effects-elements.js';
 import { Polymer, html } from '../../polymer-legacy.js';
-import { setSanitizeDOMValue, sanitizeDOMValue, setLegacyOptimizations } from '../../lib/utils/settings.js';
+import { setSanitizeDOMValue, sanitizeDOMValue, getSanitizeDOMValue, setLegacyOptimizations } from '../../lib/utils/settings.js';
 import { PropertyEffects } from '../../lib/mixins/property-effects.js';
 
 suite('single-element binding effects', function() {
@@ -341,7 +341,7 @@ suite('single-element binding effects', function() {
     assert.equal(el.customEventObject.value, 84, 'custom bound path incorrect');
     assert.equal(el.observerCounts.customEventObjectValueChanged, 1, 'custom bound path observer not called');
   });
-  
+
   test('custom notification bubbling event to property', function() {
     const child = document.createElement('div');
     el.$.boundChild.appendChild(child);
@@ -1461,6 +1461,13 @@ suite('DOM sanitization', function() {
       ['javascript', 'reflectedstring', 'attribute', el]);
   });
 
+  test('getter returns the current value', function() {
+    assert(sanitizeDOMValue instanceof Function);
+    assert.strictEqual(getSanitizeDOMValue(), sanitizeDOMValue);
+    setSanitizeDOMValue(null);
+    assert.strictEqual(sanitizeDOMValue, null);
+    assert.strictEqual(getSanitizeDOMValue(), null);
+  });
 });
 
 suite('data (im)mutability', function() {