You should never return await, just return the promise itself return result.json() as @senner007 says. The simplest use of fetch () takes one argument — the path to the resource you want to fetch — and returns a promise containing the response (a Response object). Promises are created by using APIs that return them. If you return a value, the next then() is called with that value. The response returned by the promise is a stream object which means that when we call json() method, it returns another promise. If anything goes wrong (like the JSON file cannot be found), the catch function will run. The fetch function will return a promise. Meistens wird JSON aus Datenquellen gelesen, in interaktiven Seiten aber auch geändert und als JSON-Datei serverseitig gespeichert.
In the previous example we looked at the status of the Response object as well as how to parse the response as JSON. However, sometimes deferreds pass multiple arguments to their callbacks, for example: The response returned by the promise is a stream object which means that when we call json () method, it returns another promise. Response Metadata . That isn't very informative.
Queuing asynchronous actions # You can also chain thens to run async actions in sequence. Anders als beim Lesen der JSON-Datei mit dem einfachen fetch ("data.json") braucht fetch() beim Senden von JSON die URL der Anwendung und die Optionen POST, headers und body. Here we are fetching a JSON file across the network and printing it to the console. var jsPromise = Promise.resolve($.ajax('/whatever.json')) Here, jQuery's $.ajax returns a Deferred. If we return another promise we'll get amazing things, but let's hold our horses. Promise.all([ fetch('/template.html'), fetch('/style.css'), fetch('/data.json') ]).then(render); // render method needs results of all fetches Promise.allSettled just waits for all promises to settle, regardless of the result. Promise.all takes an array of promises (it technically can be any iterable, but is usually an array) and returns a new promise..
For instance, the Promise.all below settles after 3 seconds, and then its result is an array [1, 2, 3]:
Writing the JSON File If you are expecting an XML response, you … Implicit try…catch. Call to json () method indicates that we are expecting a JSON response. Getting a response is usually a two-stage process. Calling fetch () method returns a promise. With promises
Calling fetch() method returns a promise. The code of a promise executor and promise handlers has an "invisible try..catch" around it.
Der Browser sendet den Request sofort und gibt ein Promise zurück. Wenn keine weiteren Optionen angegeben sind, ist fetch ein einfacher GET-Request und lädt den Inhalt von einer URL. The browser starts the request right away and returns a promise that the calling code should use to get the result. Let us see how this will look in out example:
Since it has a then () method, Promise.resolve () can turn it into a JavaScript promise. Ein leeres div-Tag wartet auf die fetch … First, the promise, returned by fetch, resolves with an object of the built-in Response class as soon as the server responds with headers. I haven't directly used the async/await before. The fetch API documentation on MDN states that fetch returns a Promise, and also, that async implicitly returns a Promise returns a promise (the promise will resolve to the JSON response) Because of its simplicity, fetch has quickly become the common goto method for consuming responses from API endpoints, or in the case of the example covered here, a simple JSON response from a static file. For example, the more modern AJAX replacement fetch or jQuery's $.get return promises. Can you please explain why? This is just an HTTP response, not the actual JSON. in your case there are 2 such actions: 1) fetch (which gets network resource which might take long time and reaolves it to Response once done) and 2) .json() which takes Response stream and resolves it to json object once its done (which also might be long). If you are …
JSON mit Javascript fetch einlesen. If an exception happens, it gets caught and treated as … Other metadata we may want to access, like headers, are … The response of a fetch() request is a Stream object, which means that when we call the json() method, a Promise is returned since the reading of the stream will happen asynchronously. When the JSON data is fetched from the file, the then function will run with the JSON data in the response. well, reasons are pretty straightforward: you use promises when you have async, potentially long runing operations. But if any of the promises above rejects (a network problem or invalid json or whatever), then it would catch it. The new promise resolves when all listed promises are settled, and the array of their results becomes its result. Call to json() method indicates that we are expecting a JSON response. getJSON() still returns a promise, one that fetches a url then parses the response as JSON.