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Fetch json data from url and write in a file

I’m trying to fetch Json data from a Url and then write the data in a Json File. Here is my code :

let jsondata;    
        return u.json();
    .then(function(json) {
          jsondata = json;

const fs = require('fs');

// write JSON string to a file
fs.writeFile('test.json', JSON.stringify(jsondata), (err) => {
    if (err) {
        throw err;
    console.log("JSON data is saved.");

But I’m stuck with this error as the data I want to write in my file seems to have an invalid argument while I use JSON.stringify. Someone got an idea ?

Thanks a lot for your help !

TypeError [ERR_INVALID_ARG_TYPE]: The “data” argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined


jsondata is a redundant variable. Here is a rewrite of your fetch().then().then() which leverages fs.writeFile() in the second .then().

I used node-fetch for this implementation, but it should work in a browser environment as well.

.then((response) => { 
    return response.json();
.then((json) => {
    fs.writeFile('./test.json', JSON.stringify(json), (err) => {
        if (err) {
            throw new Error('Something went wrong.')
        console.log('JSON written to file. Contents:');
        console.log(fs.readFileSync('test.json', 'utf-8'))