Excel’s IF function intimidates a lot of people, but it’s really not that conceptually difficult. The IF function determines whether a statement is true or false, and then takes one of two actions depending on the answer. Let’s look at a plain-English example. Suppose that when the sum of C2 and D2 is greater than. Create the 'header' or 'prototype' of your function. It has to have the following structure: public function 'The Name Of Your Function' (param1 As type1, param2 As type2 ) As return Type It can have as many parameters as you want, and their type can be any of Excel's basic data types or object types as Range. You may think of parameters as the 'operands' your function will act upon.

Realize that is coming from using USB 2.0 all this time.Example: One 44.9GB file would have taken an hour to move but with the USB-C card it took only five and a half minutes and that works out to 137MB/s compared to a published number I saw for 2.0 which is 10 15 MB/s.

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Custom functions enable developers to add new functions to Excel by defining those functions in JavaScript as part of an add-in. Users within Excel can access custom functions just as they would any native function in Excel, such as SUM(). This article describes how to create custom functions in Excel.

Important

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

• Office on Windows (version 1904 or later, connected to Office 365 subscription)
• Office on Mac (version 16.24 or later, connected to Office 365 subscription)
• Office on the web

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

The following animated image shows your workbook calling a function you've created with JavaScript or Typescript. In this example, the custom function =MYFUNCTION.SPHEREVOLUME calculates the volume of a sphere.

The following code defines the custom function =MYFUNCTION.SPHEREVOLUME.

Note

The Known issues section later in this article specifies current limitations of custom functions.

How a custom function is defined in code

If you use the Yo Office generator to create an Excel custom functions add-in project, you'll find that it creates files which control your functions, your task pane, and your add-in overall. We'll concentrate on the files that are important to custom functions:

File	File format	Description
./src/functions/functions.js or ./src/functions/functions.ts	JavaScript or TypeScript	Contains the code that defines custom functions.
./src/functions/functions.html	HTML	Provides a <script> reference to the JavaScript file that defines custom functions.
./manifest.xml	XML	Specifies the namespace for all custom functions within the add-in and the location of the JavaScript and HTML files that are listed previously in this table. It also lists the locations of other files your add-in might make use of, such as the task pane files and command files.

Script file

The script file (./src/functions/functions.js or ./src/functions/functions.ts) contains the code that defines custom functions and comments which define the function.

The following code defines the custom function add. The code comments are used to generate a JSON metadata file that describes the custom function to Excel. The required @customfunction comment is declared first, to indicate that this is a custom function. Additionally, you'll notice two parameters are declared, first and second, which are followed by their description properties. Finally, a returns description is given. For more information about what comments are required for your custom function, see Create JSON metadata for custom functions.

Note that the functions.html file, which governs the loading of the custom functions runtime, must link to the current CDN for custom functions. Projects prepared with the current version of the Yo Office generator reference the correct CDN. If you are retrofitting a previous custom function project from March 2019 or earlier, you need to copy in the code below to the functions.html page.

Manifest file

The XML manifest file for an add-in that defines custom functions (./manifest.xml in the project that the Yo Office generator creates) specifies the namespace for all custom functions within the add-in and the location of the JavaScript, JSON, and HTML files.

The following basic XML markup shows an example of the <ExtensionPoint> and <Resources> elements that you must include in an add-in's manifest to enable custom functions. If using the Yo Office generator, your generated custom function files will contain a more complex manifest file, which you can compare on this Github repository.

Note

The URLs specified in the manifest file for the custom functions JavaScript, JSON, and HTML files must be publicly accessible and have the same subdomain.

Note

Functions in Excel are prepended by the namespace specified in your XML manifest file. A function's namespace comes before the function name and they are separated by a period. For example, to call the function ADD42 in the cell of an Excel worksheet, you would type =CONTOSO.ADD42, because CONTOSO is the namespace and ADD42 is the name of the function specified in the JSON file. The namespace is intended to be used as an identifier for your company or the add-in. A namespace can only contain alphanumeric characters and periods.

Tip

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If you'll be testing your add-in across multiple environments (for example, in development, staging, demo, etc.), we recommend that you maintain a different XML manifest file for each environment. In each manifest file, you can:

• Specify the URLs that correspond to the environment.
• Customize metadata values like DisplayName and labels within Resources to indicate the environment, so that end users will be able to identify a sideloaded add-in's corresponding environment.
• Customize the custom functions namespace to indicate the environment, if your add-in defines custom functions.

By following this guidance, you'll streamline the testing process and avoid issues that would otherwise occur when an add-in is simultaneously sideloaded for multiple environments.

Coauthoring

Excel on the web and Windows connected to an Office 365 subscription allow you to coauthor documents and this feature works with custom functions. If your workbook uses a custom function, your colleague will be prompted to load the custom function's add-in. Once you both have loaded the add-in, the custom function will share results through coauthoring.

For more information on coauthoring, see About coauthoring in Excel.

Known issues

See known issues on our Excel Custom Functions GitHub repo.

Next steps

Want to try out custom functions? Check out the simple custom functions quick start or the more in-depth custom functions tutorial if you haven't already.

Another easy way to try out custom functions is to use Script Lab, an add-in that allows you to experiment with custom functions right in Excel. You can try out creating your own custom function or play with the provided samples.

Ready to read more about the capabilities custom functions? Learn about an overview of the custom functions architecture.

See also