Eleventy 1.0: 'addPlugin' is not a function after upgrade from 0.x

Why the error occurs

Eleventy 1.0 changed the plugin interface: it now expects each plugin to be a plain function that receives the Eleventy config object. The legacy pattern—exporting an object with an addPlugin method—was removed, so calling eleventyConfig.addPlugin on a 0.x‑style plugin throws ‘addPlugin is not a function’.

Confirmed facts from the release

• The Eleventy 1.0 release notes state that the addPlugin helper was dropped.
• No automated compatibility scanner is shipped with Eleventy.
• A temporary wrapper that re‑adds the old signature works but is unsupported and may break in future releases.

Steps to resolve the error

1. Upgrade Eleventy to 1.0 (npm install @11ty/eleventy@^1.0) and lock the version ("@11ty/eleventy": "1.0.x") to avoid accidental roll‑back.
2. Run the build (npx @11ty/eleventy) and note the full error stack trace; it will point to the plugin that triggered the addPlugin failure.
3. For each failing plugin:
   1. Check npm for a 1.0‑compatible version (look for a recent release or a changelog mentioning Eleventy 1.0).
   2. If one exists, upgrade it (npm install plugin-name@latest).
   3. If no compatible version exists, either fork the plugin and change its export to a function (module.exports = function(eleventyConfig) { … }) or replace it with an alternative that already supports 1.0.
4. Remove any temporary shim or wrapper you may have added; keep only the plain‑function plugins.
5. Run a clean build (npx @11ty/eleventy --quiet) and verify that the output is generated without errors.

What to share if you need further help

If the stack trace does not clearly identify the offending plugin, please provide the complete error output (including the line number in .eleventy.js) so the exact plugin can be pinpointed.