Utility to convert json to an excel file, based on Node-Excel-Export using a worker thread by not blocking the NodeJs event loop using async functions and options.

This is a totally fork of the json2xls , but the XLSX constructing can be CPU intensive so we are offloading the XLSX constructing using a worker thread.

Of course, when using a worker thread, the execution is about 20-25ms longer, than when we are in the event loop, so the worker thread is valid when we are generating a big dataset.

Installation 

npm install p3x-json2xls-worker-thread

Usage 

Use to save as file:

const json2xls = require('p3x-json2xls-worker-thread')
const fs = require('fs').promises

const json = {
    foo: 'bar',
    qux: 'moo',
    poo: 123,
    stux: new Date()
}
const executAsync = async() => {    
    try {
        // 
        let nodeExcelOptions = undefined
        
        /*
        The following options are supported:       
            - style: a styles xml file, see <https://github.com/functionscope/Node-Excel-Export>
            - fields: either an array or map containing field configuration:
                - array: a list of names of fields to be exported, in that order
                - object: a map of names of fields to be exported and the types of those fields. Supported types are 'number','string','bool'
        */
        if (ifSomeConditionIsTrue) {
            nodeExcelOptions = {
                fields: ['poo']
            }       
        }
        const options = {
            output: 'binary' /* default */ || 'base64',
            nodeExcel: nodeExcelOptions
        }       
        const xlsBinary = await json2xls(json, options)
        await fs.writeFile('data.xlsx', xlsBinary, 'binary');
    } catch(e) {
        // handle error
        console.error(e)
    }      
}
executAsync()

Or use as express middleware. It adds a convenience xls method to the response object to immediately output an excel as download.

const json2xls = require('p3x-json2xls-worker-thread')

const jsonArr = [{
    foo: 'bar',
    qux: 'moo',
    poo: 123,
    stux: new Date()
},
{
    foo: 'bar',
    qux: 'moo',
    poo: 345,
    stux: new Date()
}];

app.use(json2xls.middleware);

app.get('/',function(req, res) {
    res.xls('data.xlsx', jsonArr);
});

It is possible to block the event loop by using the sync function eg.:

const json2xls = require('p3x-json2xls-worker-thread')

const json = {
    foo: 'bar',
    qux: 'moo',
    poo: 123,
    stux: new Date()
}

const xlsBinary = json2xls.sync(json, {
    output: 'base64' // can be binary as well, just sugar...
})

console.log(xlsBinary)

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P3X-JSON2XLS-WORKER-THREAD Build v2026.4.123