javascript - 如何检查获取的响应是否是javascript中的json对象

Question

我正在使用 fetch polyfill 从 URL 中检索 JSON 或文本，我想知道如何检查响应是 JSON 对象还是仅文本

fetch(URL, options).then(response => {
   // how to check if response has a body of type json?
   if (response.isJson()) return response.json();
});

Answer 1

您可以检查响应的content-type，如this MDN example所示:

fetch(myRequest).then(response => {
  const contentType = response.headers.get("content-type");
  if (contentType && contentType.indexOf("application/json") !== -1) {
    return response.json().then(data => {
      // The response was a JSON object
      // Process your data as a JavaScript object
    });
  } else {
    return response.text().then(text => {
      // The response wasn't a JSON object
      // Process your text as a String
    });
  }
});

如果您需要绝对确定内容是有效的 JSON(并且不信任 header )，您可以随时将响应作为 text 接受并自己解析:

fetch(myRequest)
  .then(response => response.text()) // Parse the response as text
  .then(text => {
    try {
      const data = JSON.parse(text); // Try to parse the response as JSON
      // The response was a JSON object
      // Do your JSON handling here
    } catch(err) {
      // The response wasn't a JSON object
      // Do your text handling here
    }
  });

异步/等待

如果您使用的是 async/await，您可以以更线性的方式编写它:

async function myFetch(myRequest) {
  try {
    const reponse = await fetch(myRequest);
    const text = await response.text(); // Parse it as text
    const data = JSON.parse(text); // Try to parse it as JSON
    // The response was a JSON object
    // Do your JSON handling here
  } catch(err) {
    // The response wasn't a JSON object
    // Do your text handling here
  }
}