how to use reviver function with fetch.response.json()

Question

There is a "reviver" function that comes with JSON.parse (eg: "JSON.parse using reviver function").

How can I use this "reviver" with response.json? for instance:

fetch(url)
.then(a => a.json({reviver}))    // unfortunately not working
.then(...)

I have a workaround:

fetch(url)
.then(a => a.text())
.then(b => new Promise((resolve) => resolve(JSON.parse(b, reviver))))
.then()

but it uses one more step, which seems useless. Any better idea?

No need for that `new Promise` wrapper. And of course you don't need an extra `then` call as `JSON.parse` is synchronous, so you can just do it at the beginning of the next `then` callback. — Bergi, Oct 19 '19 at 11:27
@Bergi : I do agree with you about the wrapper. But the reviver allows to removing useless properties, resulting in a much lighter object (if huge json files). If the reviver exists with JSON.parse, why not in fetch.response.json? — allez l'OM, Oct 27 '19 at 11:18

score 9 · Answer 1 · answered Oct 19 '19 at 12:32

9

Your workaround is basically the best option but as mentioned, the extra promise is unnecessary.

fetch(url)
    .then(response => response.text())
    .then(text => JSON.parse(text, reviver))
    // ...

answered Oct 19 '19 at 12:32

Emissary

Janus · Answer 2 · 2019-10-19T11:39:30.050

-5

You could do:

fetch(url)
.then((response) => {return response.json()})
.then((json) => {console.log(json)});

Hope it helps ;)

edited Oct 19 '19 at 11:39

answered Oct 19 '19 at 11:33

Janus

The OP is trying to parse the JSON in a specific way, – Titus Oct 19 '19 at 11:44
2

The question asks how to use a _reviver_, the [optional second argument to `JSON.parse()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse#using_the_reviver_parameter), when using `response.json()`. Using `response.json()` **won't work** as it does't take a reviver argument. – Martijn Pieters Jan 27 '21 at 20:18

2 Answers2