How to read a file and convert to json array in javascript?

import fs from 'fs';

// read the file and split into rows and cells
const data = fs.readFileSync('./text.txt').toString().split('\n').map(row => row.match(/\w+/g));
// get the first row with cells as key names
const head = data.shift();

// map the rest of the rows into objects with keys from the first row
const result = data.map(row => Object.fromEntries(row.map((cell, idx) => [head[idx], cell])));
console.log(JSON.stringify(result));

The result:

/usr/local/bin/node ./read-csv.mjs
[{"key1":"data1","key2":"data2"},{"key1":"data3","key2":"data4"}]

If you need some speed boost with a big file, use Array::reduce():

import fs from 'fs';

const data = fs.readFileSync('./text.txt').toString().split('\n').map(row => row.match(/\w+/g));
const head = data.shift();

const result = data.map(row => row.reduce((obj, cell, idx) => {
    obj[head[idx]] = cell;
    return obj;
}, {}));
console.log(JSON.stringify(result));

If you need the maximum speed use for loops:

import fs from 'fs';

const data = fs.readFileSync('./text.txt').toString().split('\n').map(row => row.match(/\w+/g));
const head = data.shift();

const result = [];

for (let i = 0; i < data.length; i++) {
    const row = data[i];
    const item = result[result.length] = {};
    for (let j = 0; j < row.length; j++) {
        item[head[j]] = row[j];
    }
}

console.log(JSON.stringify(result));