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API Context

All vgplot methods are invoked within a surrounding context of evaluation. A context consists of all API methods, a coordinator, a map of named plots.

A default context is used when exported methods are called directly. This default context uses the global coordinator (returned by vg.coordinator()) and a shared namedPlots map (vg.namedPlots).

A dedicated context can be created using createAPIContext() to:

  • use an alternative coordinator to run separate Mosaic instances on the same page,
  • use a separate namedPlot maps to avoid plot name collisions across specs,
  • or extend the vgplot API with additional components and methods.



A map from plot names to plot instances. This map gets populated with a (name, plot) pair when a plot includes the name attribute. Stand-alone legend components use this map to lookup needed scale information for a plot.

A default global map is exported from the vgplot module and used as part of the default context. An isolated namedPlots instance can be created as part of a new API context.



Create a new API context that exposes vgplot methods. The following options are supported:

  • coordinator: The Mosaic coordinator to use. By default, the global coordinator (vg.coordinator()) is used. A new coordinator instance can be provided to use a separate database connector and isolated params.
  • namedPlots: The named plot map to use. By default a new, empty named plot map is created. The vg.namedPlots instance can be provided to reuse the global default map.
  • extensions: API extensions to include in the created context. All methods and properties of the extension object will be copied to returned context object, potentially overwriting existing methods.
  • ...options: Any other provided options will be included as properties of the context property of the generated API context object. This can be used to pass configuration values to extension methods.

The resulting API context object exposes the vgplot API methods, along with any properties copied from the extensions option. The API context object also includes a context property, which references an object with coordinator and namedPlots properties along with any additional options to createAPIContext.


import {
  Coordinator, createAPIContext, socketConnector
} from "uwdata/vgplot";

// create a new API context, using a coordinator with
// a dedicated socket connector to a DuckDB server
const api = createAPIContext({
  coordinator: new Coordinator(socketConnector("ws://localhost:8001/"))

// use the API context just like normal vgplot exports