React Native fetch sometimes catch a JSON parse error

Question

I'm working on a React Native application, which fetches an API response from a server. Sometimes, it returns success, but sometimes it catches an error.

The following code is my fetch function:

export default async (url, body = null, method = 'GET') => {
    let config = {
        method,
    };
    return await fetch(url, config).then((response) => {
        if (!response.ok) {
            throw Error(response.statusText);
        }
        return response.json();
    }).catch(error => {
        console.warn(error); // sometimes it was catched in here
    });
};

It was returning various error messages, e.g:

[SyntaxError: JSON Parse error: "\u302\" is not a valid unicode escape]
[SyntaxError: JSON Parse error: Invalid escape character 4]
[SyntaxError: JSON Parse error: "\u740\" is not a valid unicode escape]

I'm already checked my API response through the browser and it didn't find anything wrong with the response. I thought there was something wrong with my ES code maybe.

What is going wrong here...?

Chris Geirman · Accepted Answer · 2017-10-19 03:17:22Z

0

The \u302\ character appears to be something similar to the ^ symbol called a "COMBINING CIRCUMFLEX ACCENT" http://www.fileformat.info/info/unicode/char/0302/index.htm

And \u740\ is a "SYRIAC FEMININE DOT http://www.fileformat.info/info/unicode/char/0740/index.htm

The JSON parser just isn't able to handle these characters I guess, or at least not in the way they're presented. It looks like they're being used as an escape character, but it's hard to know since you didn't provide samples of the output that generated each error.

answered Oct 19, 2017 at 3:17

Chris Geirman

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10 Comments

Justinus Hermawan Over a year ago

Thanks for the answer. Here's sample JSON output: pastebin.com/vduDQJ8g. But, sometimes it can handle it.

Chris Geirman Over a year ago

Which error maps to this output? If you could provide the entire error message that couples to this JSON output, that would help.

Justinus Hermawan Over a year ago

It's hard to find where is exactly error location because sometimes it was parsed successfully. Is it a bug in fetch?

Chris Geirman Over a year ago

I think it's an issue with the data. So when an error occurs, capture and analyze the response along with the specific error to figure this out.

Justinus Hermawan Over a year ago

Is there any issue with async process? Perhaps the response is not completed yet, but the JSON parse process is already running so it throwed an error.

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