Add docs for google apps script

README.md

@@ -88,7 +88,7 @@ IFrame-Resizer provides an extensive range of options and APIs for both the pare
   - [Angular](https://github.com/davidjbradshaw/iframe-resizer/issues/478#issuecomment-347958630)
   - [Ember](https://github.com/alexlafroscia/ember-iframe-resizer-modifier)
   - [jQuery](https://github.com/davidjbradshaw/iframe-resizer/blob/master/docs/use_with/jquery.md)
-  - [Google Apps Script](https://stackoverflow.com/a/65724113/2087070)
+  - [Google Apps Script](https://github.com/davidjbradshaw/iframe-resizer/blob/master/docs/use_with/google_apps_script.md)
 - [Troubleshooting](https://github.com/davidjbradshaw/iframe-resizer/blob/master/docs/troubleshooting.md)
 - [Upgrade from version 3](https://github.com/davidjbradshaw/iframe-resizer/blob/master/docs/upgrade.md)
 - [Version history](https://github.com/davidjbradshaw/iframe-resizer/blob/master/CHANGELOG.md)

docs/readme.md

@@ -13,7 +13,9 @@
   - [React](https://github.com/davidjbradshaw/iframe-resizer-react)
   - [Vue](https://github.com/davidjbradshaw/iframe-resizer/blob/master/docs/use_with/vue.md)
   - [Angular](https://github.com/davidjbradshaw/iframe-resizer/issues/478#issuecomment-347958630)
+  - [Ember](https://github.com/alexlafroscia/ember-iframe-resizer-modifier)
   - [jQuery](use_with/jquery.md)
+  - [Google Apps Script](use_with/google_apps_script.md)
 - [Troubleshooting](troubleshooting.md)
 - [Upgrade from version 3](upgrade.md)
 - [Version history](../CHANGELOG.md)

docs/use_with/google_apps_script.md

@@ -0,0 +1,32 @@
+## Google Apps Script
+
+The [Google Apps Script](https://www.google.com/script/start/) platform creates a nested iframe between your app and the page it is host on. This creates a unique challenge for **iframe-resizer**, as it needs to be able to talk with the iframe it is using to calculate the page size from.
+
+This can be overcome by providing **iframe-resizer** some hints on where it needs send messages to communicate between the parent page and the iframe.
+
+### iframe
+
+The first step is to add the following line of code into your GAS application. This will send a message to the parent page, that we can then pass the detials of to **iframe-resizer**.
+
+```html
+  top.postMessage('gasFrame', '*')
+```
+
+### Parent Page
+
+The parent page needs to wait to recieve the above message before starting **iframe-resize** and then pass it the recieved referrences to the application iframe.
+
+```js
+window.addEventListener("message", (event) => {
+  if (event.data === 'gasFrame') {
+    iframeResize({
+      log: true,
+      checkOrigin: event.origin,
+      offsetHeight: 20,
+      postMessageTarget: event.source
+    }, '#myGasIframe')
+  }
+}, false)
+```
+
+The value for `offsetHeight` may need to be adjusted based on the content of your iframe.