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Creating Your Tooltip

Step 1. Add The Library

If you use yarn, you can install the library via:

yarn add vega-tooltip

With npm, you can install it as

npm install vega-tooltip

The tooltip library has the compiled tooltip library in the build directory:

vega-tooltip/build/vega-tooltip.js

If you want to manually include the library and its dependencies, you can add the following lines to your HTML script tag. Vega Tooltip works with vega and vega-lite.

<script src="https://cdn.jsdelivr.net/npm/vega@3"></script>
<script src="https://cdn.jsdelivr.net/npm/vega-lite@2"></script>

<!-- Vega Tooltip -->
<script src="https://cdn.jsdelivr.net/npm/vega-tooltip"></script>

Note that if you use Vega-Embed to deploy your visualization, you already have Vega Tooltip and don't need to do anything.

Instead of including Vega Tooltip as a script, you can import it in your bundle.

import vegaTooltip from 'vega-tooltip';

Step 2. Create A Visualization

In your HTML <body>, create a placeholder for your visualization. Give the placeholder a unique id, to which you can later refer in your JavaScript. For example:

<!-- Placeholder for my plot -->
<div id="vis"></div>

Alternatively, you can create a runtime dataflow of the visualization using vega.parse, then pass this runtime dataflow to create a View. Note that the following JavaScript code refers to the visualization placeholder by id selector (#vis).

var runtime = vega.parse(spec);
var view = new vega.View(runtime)
  .initialize(document.getElementById("vis"))
  .run();

Step 3. Set up the tooltip library

For Vega-Lite and Vega. First, create the tooltip handler.

var handler = new vegaTooltip.Handler();

Then register it when you initialize the view.

var runtime = vega.parse(spec);
var view = new vega.View(runtime)
  .tooltip(handler.call)  // note that you have to use `handler.call`!
  .initialize(document.getElementById("vis"))
  .run();

You can create your tooltip using vegaTooltip if you don't have access to the initialization. This function requires the Vega View as input.

If you get an error vegaTooltip is not a function, try to replace vegaTooltip with vegaTooltip.default. This is not necessary when you bundle your code with webpack, browserify, or rollup.

var runtime = vega.parse(spec);
var view = new vega.View(runtime)
  .initialize(document.getElementById("vis"))
  .run();

vegaTooltip(view);

Step 4. Define your tooltip in Vega or Vega-Lite

You will not see a tooltip if you skip this step.

You have to define the tooltip property in Vega or Vega-Lite. Note that if you don't use vega-tooltip, Vega will use native tooltips instead. Vega Tooltip automatically formats the data. Literal values are coerced to strings. Arrays will be shown in line. For Object values, each key-value pair is displayed in its own row in a table.

In Vega

In a Vega spec, you need to set the tooltip property on the mark for which you want to set a tooltip. If the value is on object, Vega Tooltip renders a table with one row for each key. The value with key title will not be shown as a row but instead is rendered as a heading in the tooltip.

For example, in your spec you might define a tooltip like this:

...
"tooltip": {"signal": "{'Unemployment Rate': format(datum.unemp.rate, '0.1%')}"}
...

See exampleSpecs/choropleth.json for an example.

In Vega-Lite

See https://vega.github.io/vega-lite/docs/tooltip.html#using-tooltip-channel for details on how to use the tooltip channel.

Congratulations!

Now you should be able to see a tooltip working with your visualization.

Next step: Customizing Your Tooltip