Recursively transform key/values in object, including array values

transformObj.js

/**
 * Recursively transform key/values in object, including array values
 *
 * Also can act as a basic deep clone method
 * @param {Object} obj - Object to transform
 * @param {Object} [transforms={}] - Object containing transformation functions
 * @param {Function} [transform.keys] - Function for transforming keys from 'obj'
 * @param {Function} [transform.values] - Function for transforming values from 'obj'
 * @param {Number} [level=0] - Level of recursion, passed as the 2nd argument to a transform function
 * @returns {Object} Transformed object
 *
 * @example
 * transformObj({
 *     apple: 'Green',
 *     orange: 'Orange',
 *     cherry: {
 *         color: 'Red'
 *     }
 * }, {
 *     keys: (key, level) => {
 *         return level === 0 ? `fruit_${key}` : key;
 *     },
 *     values: (value) => {
 *         return value.toUpperCase();
 *     }
 * }); // { fruit_apple: 'GREEN', fruit_orange: 'ORANGE', fruit_cherry: { color: 'RED' } }
 */
function transformObj(obj, transforms = {}, level = 0) {
    if (typeof obj !== 'object' || obj === null) {
        // nothing we can do
        return obj;
    }
    
    function convertValue(value) {
        if (Array.isArray(value)) {
            return value.map(convertValue);
        } else if (typeof value === 'object') {
            return transformObj(value, transforms, level + 1);
        } else if (transforms.values) {
            // transform value
            return transforms.values(value, level);
        } else {
            return value;
        }
    }
    
    return Object.keys(obj).reduce((result, key) => {
        let value = obj[key];
        
        if (transforms.keys) {
            // transform key
            key = transforms.keys(key, level);
        }
        
        result[key] = convertValue(value);
        
        return result;
    }, {});
}