I\'m trying to promisify JSON.parse
method but unfortunately without any luck. This is my attempt:
Promise.promisify(JSON.parse, JSON)(data).then((r
Late to the party, but I can totally understand why you might want a promisified JSON parse method which never throws exceptions. If for nothing else, then to remove boilerplate try/catch-handling from your code. Also, I see no reason why synchronous behavior shouldn't be wrapped in promises. So here:
function promisedParseJSON(json) {
return new Promise((resolve, reject) => {
try {
resolve(JSON.parse(json))
} catch (e) {
reject(e)
}
})
}
Usage, e.g:
fetch('/my-json-doc-as-string')
.then(promisedParseJSON)
.then(carryOn)
.catch(dealWithIt)
First of all, JSON.parse
is not an asynchronous function. So, don't try to promisify it.
Because I want to create a chain of promises where JSON.parse stand at the top
Then, simply create a Promise resolved with the parsed JSON object, like this
Promise.resolve(JSON.parse(data))
.then(...)
Now, to your actual question, you are getting the error,
Unhandled rejection Error: object
because, if your chain of promises is rejected, you are not handling it. So, don't forget to attach a catch handler, like this
Promise.resolve(JSON.parse(data))
.then(...)
.catch(...)
READ THIS There is a problem with the approach I have shown here, as pointed out by Bergi, in the comments. If the JSON.parse
call fails, then the error will be thrown synchronously and you may have to write try...catch
around the Promise
code. Instead, one would write it as Bergi suggested in his answer, to create a Promise object with just the data, and then do JSON.parse
on that Promise chain.
Promise.promisify is thought for asynchronous functions that take a callback function. JSON.parse
is no such function, so you cannot use promisify
here.
If you want to create a promise-returning function from a function that might throw
synchronously, Promise.method is the way to go:
var parseAsync = Promise.method(JSON.parse);
…
parseAsync(data).then(…);
Alternatively, you will just want to use Promise.resolve to start your chain:
Promise.resolve(data).then(JSON.parse).then(…);