Reproject a geojson with proj4js
npm install proj-geojson
const projgeojson = require('proj-geojson');
const fs = require('fs');
let geojson = JSON.parse(fs.readFileSync('my-file.geojson'));
const geojson2154 = projgeojson(geojson, 'EPSG:4326', 'EPSG:2154');
console.log(geojson2154);