uhh.js

const itemsJson = require('./items.json');
const FS = require('fs');
const PATH = require('path')
const SVGO = require('svgo');
const svgo = new SVGO();

let out = itemsJson.map((itemJson) => {

    let imagePath = itemJson["imagePath"]

    delete itemJson.imagePath;

    let svgoFunc = (data) => { 
        itemJson.data = {
            svg: data.data
        }
    };

    let fileData = FS.readFileSync(imagePath);

    svgo.optimize(fileData).then(svgoFunc);

    return itemJson;
});

console.log(out);