不变冲突:未全局找到fetch，也没有传递取取器，以修复环境的fetch。

Question

我正在尝试使用AWS处理程序运行一个NodeJS应用程序。我的package.json非常简单：

...
  "dependencies": {
    "aws-appsync": "^4.1.7",
    "aws-sdk": "^2.1202.0",
    "graphql-tag": "^2.12.6"
  }

当我试图运行任何我得到的东西：

Invariant Violation: 
fetch is not found globally and no fetcher passed, to fix pass a fetch for
your environment like https://www.npmjs.com/package/node-fetch.

For example:
import fetch from 'node-fetch';
import { createHttpLink } from 'apollo-link-http';

const link = createHttpLink({ uri: '/graphql', fetch: fetch });
    at new InvariantError (/Users/jamesdaniels/Code/node_modules/ts-invariant/lib/invariant.js:16:28)
    at Object.exports.checkFetcher (/Users/jamesdaniels/Code/node_modules/apollo-link-http-common/lib/index.js:65:15)
    at Object.createHttpLink (/Users/jamesdaniels/Code/node_modules/apollo-link-http/lib/bundle.umd.js:47:30)
    at Object.exports.createAppSyncLink (/Users/jamesdaniels/Code/node_modules/aws-appsync/lib/client.js:144:201)
    at new AWSAppSyncClient (/Users/jamesdaniels/Code/node_modules/aws-appsync/lib/client.js:214:72)
    at Object.<anonymous> (/Users/jamesdaniels/Code/utils/appsync.js:16:23)

该错误似乎与aws-appsync包有关。只有当我将该错误介绍到我的应用程序时，才会发生错误：

const AWS = require("aws-sdk") // Works fine
const AUTH_TYPE = require("aws-appsync").AUTH_TYPE;
const AWSAppSyncClient = require("aws-appsync").default;

// GraphQL client config
const appSyncClientConfig = {
    url: "https://xxxxxxxxxxxxxxxxx.appsync-api.eu-west-2.amazonaws.com/graphql",
    region: "eu-west-2",
    auth: {
      type: AUTH_TYPE.AWS_IAM,
      credentials: AWS.config.credentials,
    },
    disableOffline: true,
  };

// Initialise the AppSync client
const appSyncClient = new AWSAppSyncClient(appSyncClientConfig);

从依赖模块aws-appsync > apollo-link-http > apollo-link-http-common引发错误。

Answer 1

结果是错误信息告诉了我我需要知道的事情。aws-appsync不是为后端环境设计的。它适用于前端环境，在这些环境中，fetch可以在全球范围内使用。在后端，我们需要为自己的fetch创建自己的全局变量，如果我们希望它对我们安装的任何节点包可用。

解决方案是下载node-fetch，然后按照“提供全局访问”部分中的说明：

提供全局访问

要使用fetch()而不导入它，可以在节点中修补全局对象：

// fetch-polyfill.js
import fetch, {
  Blob,
  blobFrom,
  blobFromSync,
  File,
  fileFrom,
  fileFromSync,
  FormData,
  Headers,
  Request,
  Response,
} from 'node-fetch'

if (!globalThis.fetch) {
  globalThis.fetch = fetch
  globalThis.Headers = Headers
  globalThis.Request = Request
  globalThis.Response = Response
}

// index.js
import './fetch-polyfill'

// ...