Configure your Excel add-in to use a shared JavaScript runtime


Note that Excel custom functions are available on the following platforms.

  • Office on Windows
  • Office on Mac
  • Office on the web

Excel custom functions are currently not supported on iPad or in one-time purchase versions of Office 2019 or earlier.

When running Excel on Windows or Mac, your add-in will run code for ribbon buttons, custom functions, and the task pane in separate JavaScript runtime environments. This creates limitations such as not being able to easily share global data, and not having access to all CORS functionality from a custom function.

However, you can configure your Excel add-in to share code in a shared JavaScript runtime. This enables better coordination across your add-in and access to the DOM and CORS from all parts of your add-in. It also enables you to run code when the document opens, or to run code while the task pane is closed. To configure your add-in to use a shared runtime, follow the instructions in this article.

Create the add-in project

If you are starting a new project, follow these steps to use the Yeoman generator to create an Excel add-in project. Run the following command and then answer the prompts with the following answers:

yo office
  • Choose a project type: Excel Custom Functions Add-in project
  • Choose a script type: JavaScript
  • What do you want to name your add-in? My Office Add-in

Screenshot of answering prompts from yo office to create the add-in project.

After you complete the wizard, the generator creates the project and installs supporting Node components.

Configure the manifest

Follow these steps for a new or existing project to configure it to use a shared runtime.

  1. Start Visual Studio Code and open the My Office Add-in project.

  2. Open the manifest.xml file.

  3. Find the <VersionOverrides> section, and add the following <Runtimes> section. The lifetime needs to be long so that the custom functions can still work even when the task pane is closed. The resid is ContosoAddin.Url which references a string in the resources section later. You can use any resid value you want, but it should match the resid of the other elements in your add-in elements.

    <VersionOverrides xmlns="" xsi:type="VersionOverridesV1_0">
        <Host xsi:type="Workbook">
          <Runtime resid="ContosoAddin.Url" lifetime="long" />
  4. In the <Page> element, change the source location from Functions.Page.Url to ContosoAddin.Url. This resid matches the <Runtime> resid element. Note that if you don't have custom functions, you will not have a Page entry and can skip this step.

    <SourceLocation resid="ContosoAddin.Url"/>
  5. In the <DesktopFormFactor> section, change the FunctionFile from Commands.Url to use ContosoAddin.Url. Note that if you don't have action commands, you won't have a FunctionFile entry, and can skip this step.

    <FunctionFile resid="ContosoAddin.Url"/>
  6. In the <Action> section, change the source location from Taskpane.Url to ContosoAddin.Url. Note that if you don't have a task pane, you won't have a ShowTaskpane action, and can skip this step.

    <Action xsi:type="ShowTaskpane">
    <SourceLocation resid="ContosoAddin.Url"/>
  7. Add a new Url id for ContosoAddin.Url that points to taskpane.html.

    <bt:Url id="Functions.Script.Url" DefaultValue="https://localhost:3000/dist/functions.js"/>
    <bt:Url id="ContosoAddin.Url" DefaultValue="https://localhost:3000/dist/taskpane.html"/>
  8. Make sure the taskpane.html has a <script> tag that references the dist/functions.js file. The following is an example.

    <script type="text/javascript" src="/dist/functions.js" ></script>


    If the add-in uses Webpack and the HtmlWebpackPlugin to insert script tags, as add-ins created by the Yeoman generator do (see Create the add-in project above), then you must ensure that the functions.js module is included in the chunks array as in the following example.

    new HtmlWebpackPlugin({
        filename: "taskpane.html",
        template: "./src/taskpane/taskpane.html",
        chunks: ["polyfill", "taskpane", “functions”]
  9. Save your changes and rebuild the project.

    npm run build

Runtime lifetime

When you add the Runtime element, you also specify a lifetime with a value of long or short. Set this value to long to take advantage of features such as starting your add-in when the document opens, continuing to run code after the task pane is closed, or using CORS and DOM from custom functions.


The default lifetime value is short, but we recommend using long in Excel add-ins. If you set your runtime to short in this example, your Excel add-in will start when one of your ribbon buttons is pressed, but it may shut down after your ribbon handler is done running. Similarly your add-in will start when the task pane is opened, but it may shut down when the task pane is closed.

  <Runtime resid="ContosoAddin.Url" lifetime="long" />


If your add-in includes the Runtimes element in the manifest (required for a shared runtime), it uses Internet Explorer 11 regardless of the Windows or Microsoft 365 version. For more information, see Runtimes.

Multiple task panes

Don't design your add-in to use multiple task panes if you are planning to use a shared runtime. A shared runtime only supports the use of one task pane. Note that any task pane without a <TaskpaneID> is considered a different task pane.

Next steps

See also