Cesium Impl Build Deploy

CesiumJS Build and Deployment

Overview

CesiumJS ships as the cesium npm package. Unlike a single-file library it needs four static directories served alongside the bundle: Workers, ThirdParty, Assets, and Widgets. CesiumJS finds those directories through a base URL it reads at load time. Getting that base URL and the asset copy right is the whole job; getting it wrong is the dominant cause of a blank globe.

Core principle: ALWAYS do two things in a bundled CesiumJS app: copy the four static directories into the build output, and set the CESIUM_BASE_URL global to where they are served, before CesiumJS is imported. A bundler plugin does both; doing neither produces a blank globe.

When to Use This Skill

Use this skill when ANY of these apply:

• A bundled CesiumJS app renders a blank or black globe
• The console logs 404s for files under Workers, Assets, or Widgets
• A worker fails to load, or a bundler throws on a CesiumJS import
• Setting up CesiumJS in a Vite or webpack project
• Converting a Sandcastle example into a real application
• The widgets render unstyled or with a broken layout

Do NOT use this skill for runtime rendering failures unrelated to assets (cesium-errors-rendering) or for ion tokens and assets (cesium-impl-cesium-ion).

The cesium Package and Its Static Directories

npm install cesium

The package installs a prebuilt copy at node_modules/cesium/Build/Cesium. That folder contains the four directories CesiumJS loads at runtime:

| Directory | Holds | |-----------|-------| | Workers | Web Worker scripts for tiling, decoding, and geometry | | ThirdParty | Bundled third-party worker dependencies | | Assets | Textures, IAU data, and the default imagery | | Widgets | Widget CSS and images, including widgets.css |

These are NOT bundled into the JavaScript. They MUST be copied into the deployed output and served as static files.

window.CESIUMBASEURL

CesiumJS resolves every worker and asset request relative to a base URL. It reads this from the CESIUM_BASE_URL global. ALWAYS set it to the path where the four directories are served, and ALWAYS set it BEFORE the first CesiumJS import.

In a plain page with no bundler:

  window.CESIUM_BASE_URL = "/cesiumStatic";

In a bundler the value is injected at build time instead; see the Vite and webpack sections. NEVER set CESIUM_BASE_URL after importing cesium; the library reads it during module initialization and a later assignment is ignored.

Vite Setup

Use vite-plugin-cesium. It copies the four static directories into the build and configures the base URL, so the application code does not set window.CESIUM_BASE_URL itself.

npm install cesium
npm install --save-dev vite-plugin-cesium

// vite.config.js
import { defineConfig } from "vite";
import cesium from "vite-plugin-cesium";

export default defineConfig({
  plugins: [cesium()],
});

// app.js
import { Ion, Viewer } from "cesium";

Ion.defaultAccessToken = "";
const viewer = new Viewer("cesiumContainer");

ALWAYS add vite-plugin-cesium to a Vite project. Without it Vite ships the JavaScript but not the Workers, ThirdParty, Assets, and Widgets directories, and the globe is blank.

Webpack Setup

Webpack needs two plugins: copy-webpack-plugin to copy the static directories, and webpack.DefinePlugin to inject CESIUM_BASE_URL. The official cesium-webpack-example is the reference.

// webpack.config.js
const path = require("path");
const webpack = require("webpack");
const CopyWebpackPlugin = require("copy-webpack-plugin");

const cesiumSource = "node_modules/cesium/Build/Cesium";
const cesiumBaseUrl = "cesiumStatic";

module.exports = {
  output: {
    filename: "app.js",
    path: path.resolve(__dirname, "dist"),
    sourcePrefix: "",
  },
  module: {
    rules: [{ test: /\.css$/, use: ["style-loader", "css-loader"] }],
  },
  plugins: [
    new CopyWebpackPlugin({
      patterns: [
        { from: path.join(cesiumSource, "Workers"), to: `${cesiumBaseUrl}/Workers` },
        { from: path.join(cesiumSource, "ThirdParty"), to: `${cesiumBaseUrl}/ThirdParty` },
        { from: path.join(cesiumSource, "Assets"), to: `${cesiumBaseUrl}/Assets` },
        { from: path.join(cesiumSource, "Widgets"), to: `${cesiumBaseUrl}/Widgets` },
      ],
    }),
    new webpack.DefinePlugin({
      CESIUM_BASE_URL: JSON.stringify(cesiumBaseUrl),
    }),
  ],
};

DefinePlugin replaces the CESIUM_BASE_URL identifier in the CesiumJS source with the string "cesiumStatic" at build time. CopyWebpackPlugin copies the four directories to that same cesiumStatic path in dist. ALWAYS keep the two values identical; a mismatch sends every asset request to a path that does not exist.

output.sourcePrefix: "" is required so webpack does not indent the CesiumJS worker code in a way that breaks it.

ES6 Named Imports and the Widgets CSS

ALWAYS import the specific symbols by name; this lets the bundler tree-shake unused CesiumJS code.

import { Ion, Viewer, Cartesian3, createOsmBuildingsAsync } from "cesium";
import "cesium/Build/Cesium/Widgets/widgets.css";

The widgets.css import is mandatory for any app that shows Viewer widgets. Without it the Animation, Timeline, BaseLayerPicker, and other widgets render unstyled and overlap. NEVER omit the CSS import in an app that uses the Viewer.

The engine-only @cesium/engine package places its widget CSS at @cesium/engine/Source/Widget/CesiumWidget.css instead.

Sandcastle to Production Conversion

Sandcastle at sandcastle.cesium.com runs each example inside a scaffold that auto-provides the Cesium global, an HTML page, and a shared demo ion token. Production code has none of that. Convert an example in five steps.

1. Replace the implicit global with ES6 named imports. Sandcastle code uses

Cesium.Viewer; production code imports { Viewer } from "cesium".

1. Supply your own Ion.defaultAccessToken. The Sandcastle demo token is

rate-limited and NEVER valid for a deployed app.

1. Set up the bundler so CESIUM_BASE_URL is defined and the four static

directories are copied, using the Vite or webpack setup above.

1. Import cesium/Build/Cesium/Widgets/widgets.css.
2. Provide real HTML with a container element, for example

``, and a matching CSS height.

// Sandcastle form
const viewer = new Cesium.Viewer("cesiumContainer");

// Production form
import { Ion, Viewer } from "cesium";
import "cesium/Build/Cesium/Widgets/widgets.css";

Ion.defaultAccessToken = "";
const viewer = new Viewer("cesiumContainer");

Decision: Which Build Path

digraph build_path {
    rankdir=TB;
    node [shape=box, fontname="Helvetica"];
    start [label="Deploying a CesiumJS app"];
    q_bundler [shape=diamond, label="Which bundler?"];
    use_vite [label="Vite: add vite-plugin-cesium"];
    use_webpack [label="webpack: CopyWebpackPlugin\n+ DefinePlugin"];
    use_plain [label="No bundler: copy the four\ndirectories, set window.CESIUM_BASE_URL"];

    start -> q_bundler;
    q_bundler -> use_vite [label="Vite"];
    q_bundler -> use_webpack [label="webpack"];
    q_bundler -> use_plain [label="none"];
}

Common Mistakes

| Mistake | Consequence | Fix | |---------|-------------|-----| | CESIUM_BASE_URL unset or wrong | Workers, Assets, Widgets 404, blank globe | Set it to where the static directories are served | | No asset-copy step in the bundler | Worker scripts missing, blank globe | Add vite-plugin-cesium or CopyWebpackPlugin | | CESIUM_BASE_URL set after import "cesium" | The value is ignored | Set it before the first CesiumJS import | | CopyWebpackPlugin target differs from DefinePlugin value | Assets served at the wrong path | Use one shared base-URL variable | | widgets.css not imported | Widgets render unstyled and overlapping | Import cesium/Build/Cesium/Widgets/widgets.css | | Sandcastle demo token kept in production | Rate-limited, 401 on ion assets | Set your own Ion.defaultAccessToken | | Sandcastle code relying on the Cesium global | Cesium is not defined | Use ES6 named imports | | import * as Cesium from "cesium" everywhere | No tree-shaking, oversized bundle | Import the named symbols actually used | | Missing output.sourcePrefix: "" in webpack | Worker code breaks at runtime | Set sourcePrefix to an empty string |

Reference Files

• references/methods.md : the package layout, the static directories, the

base-URL mechanism, and the Vite and webpack plugin options.

• references/examples.md : complete Vite, webpack, and no-bundler setups,

plus a full Sandcastle to production conversion.

• references/anti-patterns.md : each build and deployment failure with

symptom, root cause, and fix.

Related Skills

• cesium-errors-rendering : blank-globe diagnosis beyond asset paths.
• cesium-impl-cesium-ion : Ion.defaultAccessToken and ion assets.
• cesium-syntax-viewer : the Viewer constructed once the build works.
• cesium-core-versioning : deprecated patterns in old Sandcastle code.
• cesium-impl-resium : bundling CesiumJS inside a React app.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Impertio-Studio
• Source: Impertio-Studio/CesiumJS-Claude-Skill-Package
• License: MIT

Install and usage instructions live in the source repository linked above.