在分配之前正在使用Typescript变量 [英] Typescript variable being used before assigned

问题描述

按照说明进行操作

As per instructions followed here, I'm trying to cache my endpoint URL and token from Auth0 before constructing my Apollo client:

import React from 'react';
import { ApolloClient, ApolloProvider, from, HttpLink, InMemoryCache } from '@apollo/client';
import { setContext } from '@apollo/link-context';
import { useAuth0 } from './auth/AuthContext';

const App: React.FC = () => {
	const { isLoading, getTokenSilently, getIdTokenClaims } = useAuth0();

	if (isLoading) return <Loader />;

	let endpoint: string;
	let token: string;
	const contextLink = setContext(async () => {
		if (!token) {
			token = await getTokenSilently();
		}
		if (!endpoint) {
			endpoint = await getIdTokenClaims()['https://example.com/graphql_endpoint'];
		}

		return { endpoint, token };
	});

	/**
	 * TODO: check for autorization error and remove token from cache
	 * See: https://www.apollographql.com/docs/react/v3.0-beta/api/link/apollo-link-context/
	 */

	const apolloClient = new ApolloClient({
		cache: new InMemoryCache(),
		link: from([
			contextLink,
			new HttpLink({
				uri: endpoint || '',
				headers: {
					'Content-Type': 'application/json',
					Authorization: `Bearer ${token}`
				}
			})
		])
	});

	return (
		<ApolloProvider client={apolloClient}>
			<div />
		</ApolloProvider>
	);
};

export default App;

我在上面的endpoint和token上都遇到错误TS2454(在分配变量之前使用了变量).知道我如何解决这个问题吗?

I'm getting the error TS2454 (variable is used before being assigned) for both endpoint and token above. Any idea how I can get around this?

推荐答案

您要将endpoint和token都声明为变量，但在将它们检查到setContext之前未将它们初始化为任何东西.

You're declaring both endpoint and token as variables, but not initializing them to anything before checking them inside of setContext.

    let endpoint: string;
    let token: string;
    const contextLink = setContext(async () => {
        if (!token) {
            token = await getTokenSilently();
        }
        if (!endpoint) {
            endpoint = await getIdTokenClaims()['https://example.com/graphql_endpoint'];
        }

        return { endpoint, token };
    });

尝试设置默认值:

let endpoint: string = "";
let token: string = "";

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