官方

给的答案是这样子的，发现根据里面设置的内容，并不能完成。
cocos creator2d
https://docs.cocos.com/creator/manual/zh/extension/your-first-extension.html
cocos creator3d
https://docs.cocos.com/creator3d/manual/zh/editor/extension/first.html

{
    "name": "hello-world",
    "version": "1.0.0",
    "main": "./browser.js",
    "description": "一份简单的扩展",
    "contributions": {
        "menu": [{
            "path": "Develop",
            "label": "test",
            "message": "log"
        }],
        "messages": {
            "log": {
                "methods": ["log"]
            }
        }
    }
}

这是当前的样子。无法运行。

解决方案

从编辑器里面，创建插件，生成package，然后保存。

{
  "name": "hello-world",
  "version": "1.0.0",
  "package_version":2,
  "main": "browser.js",
  "description": "一份简单的扩展",
  "author": "dema",
  "contributions": {
      "menu": [{
          "path": "Develop",
          "label": "hello_test",
          "message": "log"
      }],
      "messages": {
          "log": {
              "methods": ["log"]
          }
      }
  }
}
}

'use strict';

// 扩展内定义的方法
exports.methods = {
    log() {
        console.log('Hello dodod');
    }
};

exports.load = function () { };
 exports.unload = function () { };

注意

main ，不能用 main.js
package_version ,必须填写