I'm using fetch polyfill to retrieve a JSON or text from a URL, I want to know how can I check if the response is a JSON object or is it only text
fetch(URL, options).then(response => {
// how to check if response has a body of type json?
if (response.isJson()) return response.json();
});
You could check for the content-type of the response, as shown in this MDN example:
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
});
}
});
If you need to be absolutely sure that the content is a valid JSON (and don't trust the headers), you could always just accept the response as text and parse it yourself:
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
}
});
Async/await
If you're using async/await, you could write it in a more linear fashion:
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
}
}
