[Excel] (Custom Functions) Add new Get started article #4852
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Thank you @alison-mk for putting things together and I've reviewed and approved it! |
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| description: Get started with Excel custom functions for Office Add-ins. | |||
| title: Get started with custom functions in Excel | |||
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| title: Get started with custom functions in Excel | |
| title: Best practices for custom functions in Excel |
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| An **external service** is optional. It can give your add-in capabilities like importing data from outside the workbook. The custom functions add-in specifies how external data is incorporated into the workbook. To learn more, see [Receive and handle data with custom functions](custom-functions-web-reqs.md). | ||
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| To develop a custom functions add-in with high performance, it’s important to ensure that these three components operate in harmony. |
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I don't know that this sentence is informative. Delete?
| #### Option 1: Less nesting | ||
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| ```js | ||
| /** |
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How does this nest another custom function? I can call this with Add(1,2,3) (no custom functions).
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| ``` | ||
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| #### Option 2: More nesting |
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If this is the "bad" example, might be better to start with this, explain why it causes extra calc, and then show the better example. right now it looks like you can use either option equally well.
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| ### Excel calculation mode | ||
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| Excel has three calculation modes: Automatic, Automatic Except Tables, and Manual. For a description of these calculation modes, see [Excel Recalculation](/office/client-developer/excel/excel-recalculation). The most frequently used calculation mode for custom functions add-ins is manual calculation mode. Set the calculation mode for your add-in with the [Excel.CalculationMode enum](/javascript/api/excel/excel.calculationmode) based on your scenario. Note that automatic calculation mode may trigger recalculation often and reduce the efficiency of your add-in. |
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Might make a clearer call to action here if the goal is to make your custom functions more efficient by reading the article. Perhaps the goal is to "Refer to the article and determine which calculation mode will work best for your custom function design..."
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| To return multiple results with one function, use a dynamic array. This is usually the recommended approach because dynamic arrays only require updating a single cell to trigger recalculation for all results. To learn more about dynamic arrays in custom functions, see [Return multiple results from your custom function](custom-functions-dynamic-arrays.md). | ||
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| Another way to return multiple results is to use multiple functions and return a single result for each function. A benefit of using multiple functions is that your end user can decide precisely which formula they want to update and then only trigger recalculation for that formula. |
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Might be good to show example like in the spec. Also point out the tradeoff of how one function for multiple results is less efficient across a larger dataset. Especially if relying on an external service.
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| Another way to return multiple results is to use multiple functions and return a single result for each function. A benefit of using multiple functions is that your end user can decide precisely which formula they want to update and then only trigger recalculation for that formula. | ||
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| ### Complex data structures |
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I'm unclear on how the subsections here related to complex data structures. They look like they apply to basic data types as well.
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| ## Improve the user experience of remote data calls | ||
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| Custom functions can fetch data from remote locations beyond the workbook, such as the web or a server. For more information about fetching remote data, see [Receive and handle data with custom functions](custom-functions-web-reqs.md). To maintain efficiency when making remote data calls, consider batching external calls, minimizing roundtrip duration for each call, and including messages in your add-in to communicate delays to your end user. |
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Would be good to use the term "external service" to tie in with the graphic at the beginning and connect the dots here.
| Remote service connections can have a large impact on custom function performance. To reduce this impact, use these strategies: | ||
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| - Server-heavy processing should be handled efficiently in the remote server to shorten the end-to-end latency for a custom function. For example, have parallel computing designed on the server. If your service is deployed on Azure, consider optimization using [high-performance computing on Azure](/azure/architecture/topics/high-performance-computing). | ||
| - Reduce the number of service calls by optimizing the add-in flow. For example, only send necessary calls to a remote service. |
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I would image we could have another section about using a cache for repeat CF calls, or common calls. Check with Phoebe.
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| ### Improve user-perceived performance through add-in UX | ||
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| If a delay while calling a remote service is inevitable, consider providing messages through the add-in task pane to explain the delay to your end users. This information helps manage their expectations. The following image shows an example. |
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I would mention that they will see the "busy" text in the cell while processing, so it's not like you should always think to use the task pane. But if you fell you must might be good to point out a pattern here of how it works. You need CF runtime, set the TP image on CF entry, then turn off the TP image on CF exit. Plus the task pane has to keep track if multiple CF long processes are running (which could get complicated).
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