Custom action for plop. Appends data to JSON files

plopfile.js

const fs = require('fs-extra');
const methods = {}, priv = {};
// Private methods to do string replacement. Not optimized and cummulative trying to keep it simple.
// far better options here: https://stackoverflow.com/questions/5069464/replace-multiple-strings-at-once
priv.replaceObj = function(value, vars) {
    let obj = value;
    Object.keys(obj).forEach(function(item) {
        obj[item] = priv.replaceStr(obj[item], vars);
    });
    return obj;
}
priv.replaceStr = function(value, vars) {
    let val = value;
    Object.keys(vars).forEach(function(var_key) {
        let find = new RegExp( '{{' + var_key + '}}' , "g");
        val = val.replace(find, vars[var_key]);
    });
    return val;
}
// Replaces in string or all object values. Arrays not considered
priv.replace = function(value, vars) {
    return (typeof value === "object") ? priv.replaceObj(value, vars) : priv.replaceStr(value, vars);
}

/**
 * Inserts entries into JSON arrays or objects
 *
 * To use with objects be sure to pass the property JSONEntryKey,
 * otherwise the value is inserted as arrays
 * @method
 * @param  {string}   file  filename with the JSONKey
 * @param  {string}   key   JSON attribute (the array or object) to append to
 * @param  {string || object}   value The string or object to appendJSON
 * @param  {object}   vars  User input on prompts passed by plop
 * @param  {Function} cb    callback, after file has been saveSidebarRef
 * @return {callback(err)}   Async callback with err or null if success.
 */
methods.appendJSON = function (config, vars, cb) {
    fs.readJSON(config.JSONFile, {}, (err, json) => {
        // Object or array
        let attribute_name = config.hasOwnProperty("JSONEntryKey") ?
                priv.replaceStr(config.JSONEntryKey, vars) : null;

        // Validate JSON is correct - we don't autoadd only append top level
        if (!json.hasOwnProperty(config.JSONKey)) {
            return cb('JSON has no property: ' + config.JSONKey);
        }
        // Follow plop style, don't override existing entries unless force is true.
        if (!config.force && attribute_name && json[config.JSONKey].hasOwnProperty(attribute_name)) {
            return cb("Attribute: " + attribute_name + ' already exist in ' + config.JSONKey)
        }
        // Do replacements in value (value can be a string or an object)
        let insert_val = priv.replace(config.JSONEntryValue, vars);
        // Choosing object (key:value) OR push(value)
        if (attribute_name) {
            json[config.JSONKey][attribute_name] = insert_val;
        } else {
            json[config.JSONKey].push( insert_val);
        }

        fs.writeJSON(config.JSONFile, json, {spaces: 2}, err => {
            cb(err);
        });
    });
}
// Finally the action type.
plop.setActionType('appendJSON', function(answers, config, plop) {
        return new Promise((resolve, reject) => {
            methods.appendJSON(
                config,
                answers,
                function callback(err){
                    if (!err) {
                        resolve('JSON File has been updated');
                    } else {
                        reject('appendJSON failed: ' + err);
                    }
                }
            );
		});
});

plopfile_example.js

plop.setGenerator( "package", {
        description: "Creates a new package",
        prompts: [
            {
                type: "input",
                name: "name",
                message: "What is your package name?"
            }
        ],
        actions: [
            {
                type: "add",
                path: "lib/{{name}}/{{name}}.js",
                templateFile: ".plop-templates/module.js"
            },
            { // push an object in array packages
                type: 'appendJSON',
                JSONFile: "config.json",
                JSONKey: "packages",
                JSONEntryValue: { "mountpath": "/{{name}}","module": "{{name}}/{{name}}_router"}
            },
            { // adds an attribute: {{name}}, with value: {object} in object packages
                type: 'appendJSON',
                JSONFile: "config.json",
                JSONKey: "packages",
                JSONEntryKey: "{{name}}",
                JSONEntryValue: { "mountpath": "/{{name}}","module": "{{name}}/{{name}}_router"}
            }
        ]
    });