BokehJS is the in-browser client-side runtime library that users of Bokeh ultimately interact with. This library is written primarily in CoffeeScript and is one of the unique things about the Bokeh plotting system.

BokehJS Motivations

When researching the wide field of JavaScript plotting libraries, we found that they were all architected and designed to integrate with other JavaScript. If they provided any server-side wrappers, those were always “second class” and primarily designed to generate a simple configuration for the front-end JS. Of the few JS plotting libraries that offered any level of interactivity, the interaction was not really configurable or customizable from outside the JS itself. Very few JS plotting libraries took large and streaming server-side data into account, and providing seamless access to those facilities from another language like Python was not a consideration.

This, in turn, has caused the developers of Python plotting libraries to only treat the browser as a “backend target” environment, for which they will generate static images or a bunch of JavaScript.


BokehJS is intended to be a standalone, first-class JavaScript plotting library and interaction runtime for dynamic, highly-customizable information visualization.


BokehJS is a standalone JavaScript library for dynamic and interactive visualization in the browser. It is built on top of HTML5 canvas, and designed for high-performance rendering of larger data sets. Its interface is declarative, in the style of Protovis, but its implementation consists of a reactive scene graph (similar to Chaco).

More information is available at Developing with JavaScript.

CSS Class Names

The CSS for controlling Bokeh presentation are located in a bokeh.css file that is compiled from several separate .less files in the BokehJS source tree. All CSS classes specifically for Bokeh DOM elements are prefixed with the string bk-. For instance some examples are: .bk-plot, .bk-toolbar-button, etc.

Furthermore, BokehJS ships with its own version of Bootstrap. To prevent name collisions, the version of Bootstrap CSS that Bokeh uses has been entirely prefixed with the prefix bk-bs-.