For more information on Panels, see also:


When you log metrics, hyperparameters, or other values in Comet, you can easily plot those values using the built-in charts. However, you may want to alter the chart in a subtle way. For example, perhaps you want the lines slightly thicker in the display. Or perhaps you want to display your data in a manner that is very different from any of the built-in charting options. What can you do?

Now you can easily create your own visualizations with your Comet data and re-use them on any of your Projects or Experiments. This section will explore how to do this. First, we write a simple Panel from scratch, and then we deconstruct a pre-written Panel.

Panel Code

To make a snappy user experience in the browser, we will write our Panel in JavaScript.


Even if you may not be very familiar with JavaScript, it is possible to either tweak an existing Panel, or to write your own Panel from scratch. Most everything you need is contained on this page or linked to from here. And we are here to help!

We will create a new Panel from the Panels Gallery as described in Comet's User Interface. Briefely, you will go to the Panels Gallery on the Project View and click on "Create New". You should then see a screen similar to the following:

Once you are on this screen, you are now ready to write the code. (There is some default code provided on the creation of a new Panel, but you can simply select it all with CONTROL+A and press Delete). Your new Panel code only needs these two things:

  1. A JavaScript class named MyPanel
  2. A draw(experimentKeys, projectId){} method that takes an array of experiment keys and project ID

That's it! We have also defined a Comet.Panel to extend that contains additional functionality. You use it like this:

javascript class MyPanel extends Comet.Panel { draw(experimentKeys, projectId) { // Your code here } }

In the tradition of introductory programming exercises, let's explore a "Hello world" Panel. We take the basic template from above, and add our instructions to print "Hello, world!" in our panel. We will use this.print() to display the message.


In JavaScript, this is like self in Python. That is, it is the reference to the current instance.

We'll also use the HTML <h1> tag to make our message large and bold.

javascript class MyPanel extends Comet.Panel { draw(experimentKeys, projectId) { this.print("<h1>Hello, world!</h1>"); } }


this.print() will display a message in the Panel. console.log() will display a message in the console area on the bottom right.

If you write (or copy and paste) the above code into the Panel Code section, and click on the green arrow button (or press CONTROL+ENTER) you should see the following:

Now, you can save your Panel by clicking on the save button (or pressing CONTROL+S), which will prompt you for a name:

Name your Panel something like "Hello World", and click "Save". The first time you save a new Panel, you'll be asked to capture a thumbnail of your Panel. You can either select a portion of the screen, or upload your own image:

If you press "Done" then you will go back to the Panels Gallery. Now you can add a "Hello World" Panel to your project by clicking the "+ Add" button in the Panels Gallery. A window will appear giving you the chance to set some options (discussed in the next section). For now, just press "Done".

Your Project View should now include your "Hello World" Panel:

In the next section, we'll explore the idea of an "option."


It would be very painful if you had to edit code to have slight variations of a Panel. For example, imagine that you wanted to plot the metric "acc" in one chart, but the metric "loss" in another. To allow the Panels to be more abstract, we have provided the Panels with the idea of options.

To provide these options that can be changed when creating a Panel and without changing code, you only need to define a JavaScript object in the MyPanel instance named options. Typically, you will define your options in the setup method, as shown below. These are default values that can be overridden by the user when creating a new instance of the Panel.

```javascript class MyPanel extends Comet.Panel { setup() { // Your setup code here this.options = { // Your default options here } }

draw(experimentKeys, projectId) { // Your code here } } ```

As a concrete example, let's change the "Hello World" Panel to include a setup() method with the option "message":

```javascript class MyPanel extends Comet.Panel { setup() { this.options = { message: "Hello, world!" } }

draw(experimentKeys, projectId) { this.print(<h1>${this.options.message}</h1>); } } ```

If you try this Panel, you'll see exactly the same result as before. However, there is a big difference: you can now add two instances of the "Hello World" Panel to your Project View, and make each one say something different by merely changing the options when you add the Panel to your Project:

Specifically, the steps are:

  1. Create the Hellow World Panel, using the option "message"
  2. Add one of these Panels to your Project
  3. Add another of these Panels to your Project, this time changing the message to something else

The Comet.Panel Class

When you extend from Comet.Panel you get additional functions, including:

  • this.print(object, newLine) - print text in main Panel area; newLine == true means follow with newline
  • this.getOption("name", default) - get a name from the options (return null if not defined); return default if not found
  • this.clear(divId) - clear all of the print()ed items in the panel area, or give it the ID of a div to clear
  • this.drawOne(experimentKey) - conventional method for single experiment drawing code
  •, options, parentId) - create a HTML select widget for selecting widgets; calls this.drawOne(selectedItem)
  • this.getColor(experimentKey) - get the color associated with this experiment


Your class must be named MyPanel to use these features. You can, of course, do your own JavaScript processing.

In addition, you can also define the following metjhods to gain additional functionality:

  • update(experimentKeys, projectId) {} - method to define code that will not clear the panel, but can be used to update existing UI components (see below)

The Panel.draw() Method

A Panel's draw() method receives two things:

  • an array of experiment keys
  • a Project ID

The array of experiment keys is one of three things, in this order:

  • if a Panel filter is set, the experiments keys are all those matching the Panel filter
  • if a Project View filter is set, the experiment keys are all those matching the Project Filter
  • if no filter is set, the experiment keys are those visible in the Project experiment table

Note that there are two ways that an experiment is visible in the experiment table on the Project View:

  • the experiment must be on the current table page (the table shows a limited number of experiments per page)
  • the experiment must not be hidden (the "eye" icon must not be grayed out)

If you want to always process all experiments (or programmatically select a subset from all of them), you can instead use the Project ID to get all of the experiments in a Project, like this:

javascript draw(experimentKeys, projectId) { this.api.experimentsByProjectId(projectId).then(experimentKeys => { // process all Project experimentKeys here }); }

If you are processing the array of experiment keys (experimentKeys) then be aware that these can change and a refresh will occur on any of these events:

  • you change the experiment table page limit (number of experiments per page)
  • you change, add, or remove the experiment filter
  • you change any experiment's hide/show status (either by clicking the "eye" icon in the experiment table, or by selecting experiments to hide via another Panel)

If you are instead processing the experiments via the projectId key, then you will probably want to flip the toggle on the Panel instance editor to make it "static":

The Panel.update() Method

Here is a template using the Panel.update() method. We restructure the code so that the Panel.draw() creates a Plotly plot instance, and a place to cache a set of experiment keys. Panel.update() is called whenever new data is received, but we make it so that the update method only processes experiments that it hasn't seen before.

```javascript class MyPanel extends Comet.Panel { ...

draw(experimentKeys, projectId) { Plotly.newPlot(, [], this.options.layout); this.cached_experiments = []; this.draw(experimentkeys, projectId); }

update(experimentKeys, projectId) { experimentKeys = experimentKeys.filter(key => ! this.cached_experiments.includes(key)); this.api .experimentMetricsForChart( experimentKeys, this.options.metrics, this.options.parameters ) .then(results => { Object.keys(results).forEach(experimentKey => { ... this.cached_experiments.push(experimentKey); Plotly.addTraces(, data); }); }); } } ```

Note that if you don't have a Panel.update() method that the entire Panel HTML area will be cleared and Panel.draw() will be called each time new data is available. You can use the Panel.update() method to do more intelligent processing for a snappier user interface experience.

JavaScript API

The Comet.Panel class also creates an interface to Comet's JavaScript SDK through this.api. This has all of the methods needed to access your data, plus some that are especially useful in creating a Panel. There are a few methods of special interest here:

  •, data) - save to this Panel instance's persistent memory
  • this.api.getFromStore(name) - get an item from this Panels' persistent memory

For more details on the complete library, please see Comet's JavaScript SDK.

In addition, there are a variety of Comet open source JavaScript libraries that you can use (and build upon) via the Resources Tab.

Single Experiment Workaround is designed to allow you to select a single experiment from the Project, and works as follows:

```javascript class MyPanel extends Comet.Panel { // Define your draw method like this draw(experimentKeys, projectId) { if (experimentKeys.length > 0) {"Select an experiment: ", experimentKeys); this.drawOne(experimentKeys[0]); } }

drawOne(experimentKey) { // Insert code here to do something with one experiment key } } ```


Note that console.log() displays the items in the Console portion of the user interface.

Full Example

Here is a basic line chart example using Plotly:

```javascript class MyPanel extends Comet.Panel { setup() { // Your setup code here this.options = { // Your default options here metrics: ["loss", "acc"], parameters: [], layout: { showlegend: true, legend: { orientation: 'h', }, title: { text: "My Panel Title", } }, }; }

draw(experimentKeys, projectId) { // Your code here Plotly.newPlot(, [], this.options.layout); this.api.experimentMetricsForChart( experimentKeys, this.options.metrics, this.options.parameters) .then(results => { Object.keys(results).forEach(experimentKey => { const name = this.api.experimentName(experimentKey).then(name => { results[experimentKey].metrics.forEach(result => { const data = { y: result.values, x: result.steps, name: ${name} ${result.metricName}, }; Plotly.addTraces(, data); }); }); }); }); } } ```

In this example, we've defined this.options that defines a list of metrics and parameters to chart, and a layout object. We are using Plotly, so we can put anything there that Plotly can use. See Plotly for more information.

Any option can be overridden by the user when they instantiate the Panel on their own page. Therefore, you can easily use the same code for plotting multiple items by simply changing the options.

For more details on using Comet Panels, please see Panels.

JavaScript Tips

JavaScript is designed to give a performant experience on the web. If you adapt your coding style to the way of the JavaScript, you will be rewarded with a fast-loading, snappy experience. But it does take a little bit of extra work.

Comet's JavaScript SDK is written using Promises. These are JavaScript objects that represent a promise to complete some code. The code might be finished already, or you might have to await for it to complete. You can do whatever you would like, but JavaScript has some simple syntax for running multiple functions in parallel.

Let's take a look at some examples. Often, you may want to get some data, and then process it, and finally display it. Ideally, you can do this all in parallel. The example from above does exactly that. Consider that code again:

javascript 1 class MyPanel extends Comet.Panel { 2 ... 3 draw(experimentKeys, projectId) { 4 // Your code here 5 Plotly.newPlot(, [], this.options.layout); 6 this.api.experimentMetricsForChart( 7 experimentKeys, this.options.metrics, this.options.parameters) 8 .then(results => { 9 Object.keys(results).forEach(experimentKey => { 10 const name = this.api.experimentName(experimentKey).then(name => { 11 results[experimentKey].metrics.forEach(result => { 12 const data = { 13 y: result.values, 14 x: result.steps, 15 name: `${name} ${result.metricName}`, 16 }; 17 Plotly.addTraces(, data); 18 }); 19 }); 20 }); 21 }); 22 } 23 }

Some important things to note:

  • Line 5 displays an empty Plotly chart, which will get added to in parallel
  • Lines 6 and 10 represent Promises that are followed by a .then() method that says what to do after the promise is resolved
  • Line 17 adds the result of each individual chain of processing to the chart

This is the ideal method of JavaScript processing for the web. However, you can't always work in such a style. For example, if you wanted to find the average of all of a particular metric, then you must collect all of those metrics first. Here is an example of how to do serial processing:

javascript 1 class MyPanel extends Comet.Panel { 2 ... 3 async draw(experimentKeys, projectId) { 4 const data = await this.collectData(experimentKeys); 5 this.print(`<p>Average: ${avg(data)}</p>`); 6 } 7 }

Things to note:

  • Line 3 has added the async keyword in front of the draw() method. This is necessary for any function/method that needs to await on a result
  • Line 4 has an await keyword in front of a method call

That's it, for the structure. Let's now take a look at how collectData() could be written. Consider that you have logged an "other" value (not a metric or parameter) using experiment.log_other("x", value) for all of the experiments in this project. Now we want to fetch all of those values, and average them.

javascript 1 async collectData(experimentKeys) { 2 const values = await Promise.all( 3 => { 4 return this.api.experimentOther(experimentKey, "x"); 5 }) 6 return values.filter(v => typeof v == "string"); 7 );

Things to note:

  • Line 1, again we add async
  • Line 2, we perform an await on a Promise.all(, a very common pattern
  • Line 6, a bit of technical detail, to filter out NaN and other bad values

The last example blocks to get all of the values, before proceeding. This is different from the first example. If your code takes a while to process, you can put a this.print("<h2>Processing...</h2>") before the collection, and this.clear() after it.

For more examples, see the shared code examples in the Gallery.

Working with Plotly

Plotly is a free and open source JavaScript library built on d3.js and

As shown above, for performance reasons, you typically want to create the Plot and incrementally add traces to it.

Plotly has many options, such as limiting the X and Y axis using the layout.xaxis.range and layout.yaxis.range values, like this:

javascript class MyClass extends Comet.Panel { draw(experimentKeys, projectId) { const data = ... // get some data here const layout = { xaxis: {range: [1, 10]}, yaxis: {range: [5, 7]} }; Plotly.newPlot(, data, layout); } }

Here are some of the most useful links for working with Plotly:

Working with other JavaScript Libraries

There really is no limit to what you can build with Comet Panels. Here are some additional links to JavaScript libraries that you might find useful:

Standalone JavaScript Example

To use Comet’s JavaScript SDK programming standalone interface, you will first need to get a Comet API key.

To use the JavaScript SDK outside of Comet Panels, you'll need to load the library. You can do that in HTML like:



Once the Comet JavaScript library is loaded, then you can use it as described in the previous section. Here is a brief example (substituting your Comet API key in the following):

```javascript const comet_api = new Comet.API("COMET_API_KEY");

comet_api.experimentMetricsForChart( experimentKeys, ["metric1", "metric2"], ["param1", "param2"]) .then(results => { Object.keys(results).forEach(experimentKey => { const name = comet_api.experimentName(experimentKey).then(name => { results[experimentKey].metrics.forEach(result => { const data = { y: result.values, x: result.steps, name: ${name} ${result.metricName}, }; // do something with data }); }); }); }); ```

Frequently Asked Questions

1. Which experiment keys does the Panel have access to?

Each Panel can pick what experiments to operate on. See The Panel.draw() Method for more details.

2. Can I create URL links to experiments from a Panel?

Yes, you can include any HTML, and URL links will work fine in a Panel. There is one thing to keep in mind: always provide a `target` for your href like this:

&a href="" target="_blank">TEXT&a> or &a href="" target="_top">TEXT&a>

You should use "_top" (replaces the current page) or "_blank" (opens a new tab) for the `target` attribute.

Note that Panels run in HTML iframes, and don't have access to your account. For example, you aren't logged in in the iframe, and so your data is safe and secure.

Additional Information

For more information, please see: