create version file.

createVersionFile.js

const git = require('git-rev'),
    package = require('./package.json'),
    fs = require('fs');

console.log('\n------------------- create version.json file -------------------\n');

Promise.all([
    new Promise((resolve, reject) => {
        git.short(hash => {
            if(hash) {
                resolve(hash);
            } else {
                reject('git short hash could not be read');
            }
        });
    }),
    new Promise((resolve, reject) => {
        git.long(hash => {
            if(hash) {
                resolve(`${package.version}_${hash}`);
            } else {
                reject('git long hash could not be read');
            }
        });
    }),
    new Promise((resolve, reject) => {
        git.branch(branch => {
            if(branch) {
                resolve(branch);
            } else {
                reject('git branch could not be read');
            }
        });
    }),
    new Promise((resolve, reject) => {
        git.tag(tag => {
            if(tag) {
                resolve(tag);
            } else {
                reject('git tag could not be read');
            }
        });
    })
]).then(data => {
    const [short, version, branch, tag] = data,
        result = JSON.stringify({
            application: package.name,
            version,
            short,
            branch,
            tag,
            buildTime: new Date()
        });

    console.log(result);

    fs.writeFile('./dist/version.json', result, 'utf-8', err => {
        if(err) {
            throw err;
        }

        console.log('\n------------------- version.json created -------------------\n');
    });
});