獲取 API 未在 Node.js 中提供響應數據

Question

我一直在嘗試解決這個問題，但它給了我這個： ReferenceError: json is not defined

這是我的代碼：

const fetch = require('node-fetch');

function makeAFile(text){
    fetch("http://bin.shortbin.eu:8080/documents", {
        method: "post",
        body: 'hey wassup'
    })
    .then(res => res.json())
    .then(json => console.log(json))
    .catch(err => console.log(err))
    return json
}

console.log(makeAFile('nope'))

Answer 1

您需要了解異步調用的工作原理。

const fetch = require('node-fetch');

function makeAFile(text){
    fetch("http://bin.shortbin.eu:8080/documents", { // this is async call
        method: "post",                              // might give result later in time
        body: 'hey wassup'
    })
    .then(res => res.json())
    .then(json => console.log(json))
    .catch(err => console.log(err))
    return json                     // JSON is not defined and will be return just after 'Fetch' is called which is 'undefined'

console.log(makeAFile('nope'));

要使您的代碼同步，您應該像這樣使用 async await：

const fetch = require('node-fetch');

async function makeAFile(text){
    let res = await fetch("http://bin.shortbin.eu:8080/documents", { // await helps you to wait here to make your code sync
        method: "post",                              
        body: 'hey wassup'
    })
     const json = res.json()
     
    return json ;                                
}

try {
const response = await makeAFile('nope')); //use try catch to catch error
console.log(response);
}
catch (error) {
console.log(`Error ${error}`);
} 

Answer 2

您似乎對如何從異步調用返回數據感到困惑。 你可以使用這樣的回調來做到這一點：

const fetch = require('node-fetch');

function makeAFile(text){
  return fetch("http://bin.shortbin.eu:8080/documents", {
    method: "post",
    body: text
  })
  .then(res => res.json())
  .catch(err => { console.error(err) })
}

makeAFile('nope').then((result) => console.log(result));

你可以在這里閱讀更多信息；

編輯：使用async/await提供解決方案

async function makeAFile (text) {
  try { 
    const res = await fetch("http://bin.shortbin.eu:8080/documents", {
      method: "post",
      body: text
    })
    return res.json();
  } catch (err) {
    console.error(err);
  }
}

// Define an anonymous async function to allow await statements inside
(async () => {
  // this "await" here is important
  const result = await makeAFile('nope');
  console.log(result);
  // now result is store inside of "result"
})();

Answer 3

您無權在外部訪問json then回調。 只需讓您的 function async ，這樣您就可以訪問它並且外部上下文代碼可以等到您的 function 將被解決或拒絕：

const fetch = require('node-fetch');

async function makeAFile(text){
    const res = await fetch("http://bin.shortbin.eu:8080/documents", {
        method: "post",
        body: 'hey wassup'
    })
    const json = res.json()
    console.log(json)
    return json
}

並稱之為：

try {
  const result = await makeAFile('nope')
  console.log(result)
} catch(err) {
  console.log(err)
}

或者

const result = makeAFile('nope').then(result => {
  console.log(result)
})
.catch(err => {
  console.log(err)
});

Answer 4

const fetch = require('node-fetch');

function makeAFile(text){
    jsonOut = ''
    fetch("http://bin.shortbin.eu:8080/documents", {
        method: "post",
        body: 'hey wassup'
    })
    .then(res => res.json())
    .then(json => jsonOut = json)
    .catch(err => console.log(err))
    return jsonOut
}

console.log(makeAFile('nope'))

您無法訪問 promise 中的值。 只需檢查此代碼