Common workflows and tips

Please also read our page about a few JavaScript quirks that you might encounter while using JavaScript in Iodide.

Running Async code

When you are running code in an Iodide notebook, if you run a code chunk that returns a Promise Iodide will pause further evaluation until the Promise resolves. This demo notebook gives a simple example of the concept. and this notebook shows how the idea can be used with an immediately invoked function expression to fetch data programmatically.

This feature of Iodide may be used to simplify async workflows, particularly when you wish to share a notebook report, which will automatically run code in the notebook.

Getting data into an Iodide notebook

Iodide can use JavaScript and standard browser APIs to download data from public URLs on the web. As a convenience, we also provide a “fetch chunk” in IOMD, which allows you to load data using a shorthand syntax. You can read more about IOMD fetch chunk syntax in the fetch chunk section of the IOMD docs.

From a remote server

It's possible to download data from a remote server using a browser APIs or a fetch cell. Examples are given in the fetch chunk section of the IOMD docs.

CORS problems

One of the most common problems people encounter when attempting to load data into Iodide from a remote server are issues with CORS settings, which can restrict the ability of Iodide to download data from some other websites. Unfortunately, for security reasons browsers make it impossible to surface CORS errors in a web app, so Iodide cannot give you the guidance you need directly, but if you have trouble loading a data file from a third party server, this is very likely to be the reason why. To check, you can open your browser's developer tools (press ctrl+shift+i); in case of a CORS issue, you will see a message like:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at {URI of resource you tried to load}.
(Reason: CORS request did not succeed).

To work around CORS errors, you need to upload your data to a server that does not impose restrictions on resource sharing. We recommend using either the Iodide server for storing data (see below), or using a GitHub Gist, which will allow you to upload files that can be downloaded within Iodide. After uploading your data into a gist, you can access the data by copying the URL for the "raw" version of your gist, which can be accessed at{your user name}/{your gist id}/raw

Uploading data to an Iodide notebook

Note: during our alpha period, files larger than 10MB cannot be uploaded.

If you want to work with data stored on your local machine or if you are encountering CORS problems while attempting to use a dataset from a remote server, you may upload data directly to Iodide.

uploading files directly

Data is uploaded on a per-notebook basis—rather than uploading data to your user account, you upload it to a specific notebook. There are two ways to do this.

To create a new notebook with certain files attached, drop the files anywhere on the Iodide homepage.

To add files to an existing notebook, open the notebook and click on the hamburger menu icon near the top-left of the page, then click Manage Files. The file management modal will appear. By default, you will be in the Manage Files tab. Click Add Files and select any number of files to upload. Once the files finished uploading, they will appear in a list alongside other files associated with that notebook. Click Delete at any time to delete a file.

To access this file from your notebook, you would use a fetch cell with the syntax --

%% fetch

-- where TYPE is the type of the file ("text", "json", "arraybuffer", or "blob"), VARNAME is the variable into which you want to load the data, and FILE_NAME is the name of the file you uploaded.

This notebook shows how to load and use an image blob.

scheduling file uploads

Additionally, from the file management modal you can also add file sources, which allow you schedule file downloads from URLS on the Iodide server. To do so, click on the manage file sources tab in the file management modal tab bar. Enter a URL as an input, a filename as an output, and an automatic update interval (with the options: "never", where the file source must be manually updated; "daily", where the file source is updated once a day; and "weekly" where the file source is updated once a week). The file sources API will download the file at the specified URL and save the file to the Iodide server according to the update interval. The resulting file will be available to the notebook just like any other file.

Readers will not be able to see what file sources the author has added, but can utilize the saved file outputs in the notebook as files. There are a few intended use cases for file sources:

  1. sometimes a notebook author may want to utilize a dataset from a URL that may have sensitive information in the URL, such as an API key. Using a file source will allow the author to fetch and save the data without exposing that information.
  2. sometimes an author may want to cache data from a URL that is not available due to CORS restrictions, but wants the dataset to be refreshed periodically without having to manually add the data themselves.

Manipulating the DOM (for e.g adding plots)

Some plotting libraries (like d3, or Plotly) require a DOM element to be available before you can plot. The easiest way to do this is to add a <div> into a Markdown cell and then select the element using browser APIs or functions from your preferred library:

%% md
<div id=’plot-target’></div>

%% js
elt1 = document.getElementById("plot-target") // browser API, one option...
elt2 = document.querySelector("#plot-target") // browser API, another option
$("#plot-target") ... // jQuery"#plot-target") ... // d3

You can always manipulate the DOM in Markdown cells as if your notebook were a static web page. Anything defined in a Markdown cell is fair game for DOM manipulation using the browser's document API methods.