Azure Function Linux Node.js使用@azure/storage-blob报错：Cannot read property 'startsWith' of undefined

问题场景 #

本地测试Azure Node.js Linux函数时，使用以下代码初始化BlobServiceClient：

import { BlobServiceClient } from "@azure/storage-blob";

const connectionString = process.env[
  "AZURE_STORAGE_CONNECTION_STRING"
] as string;

export const blobServiceClient =
  BlobServiceClient.fromConnectionString(connectionString);

执行rm -rf dist/ && npm run-script build && func start后，出现以下核心错误：

[2023-08-15T09:06:03.568Z] Worker was unable to load function sealworker: 'Cannot read property 'startsWith' of undefined'
[2023-08-15T09:06:03.568Z] Stack: TypeError: Worker was unable to load function sealworker: 'Cannot read property 'startsWith' of undefined'
[2023-08-15T09:06:03.568Z]     at extractConnectionStringParts (/Users/john/myApp/code/seal/azure_function/node_modules/@azure/storage-blob/dist/index.js:13654:26)
[2023-08-15T09:06:03.568Z]     at Function.fromConnectionString (/Users/john/myApp/code/seal/azure_function/node_modules/@azure/storage-blob/dist/index.js:24328:32)

尽管用as string做了TypeScript类型断言，仍触发该错误。

错误原因 #

TypeScript的as string仅为类型提示，不会改变运行时变量的实际值。报错本质是运行时process.env.AZURE_STORAGE_CONNECTION_STRING为undefined，导致BlobServiceClient.fromConnectionString接收到undefined参数，内部调用startsWith方法时触发类型错误。

解决步骤 #

1. 检查本地环境变量配置文件 #

Azure Functions本地开发依赖local.settings.json加载环境变量，确保文件中包含正确的连接字符串配置：

{
  "IsEncrypted": false,
  "Values": {
    "AzureWebJobsStorage": "xxx",
    "FUNCTIONS_WORKER_RUNTIME": "node",
    "AZURE_STORAGE_CONNECTION_STRING": "你的存储账户连接字符串"
  }
}

注意：修改该文件后需重启func start服务，新配置才会生效。

2. 增加运行时校验 #

在代码中提前判断变量是否存在，避免undefined传入SDK，同时输出明确错误信息：

import { BlobServiceClient } from "@azure/storage-blob";

const connectionString = process.env.AZURE_STORAGE_CONNECTION_STRING;

// 运行时校验，提前抛出明确错误
if (!connectionString) {
  throw new Error("环境变量AZURE_STORAGE_CONNECTION_STRING未配置或加载失败");
}

export const blobServiceClient = BlobServiceClient.fromConnectionString(connectionString);

3. 验证环境变量加载情况 #

可临时添加日志打印，确认环境变量是否被正确读取：

console.log("AZURE_STORAGE_CONNECTION_STRING:", process.env.AZURE_STORAGE_CONNECTION_STRING);

启动函数后查看控制台输出，若打印为undefined，说明local.settings.json未被正确加载或配置有误。

内容的提问来源于stack exchange，提问作者Kid_Learning_C