deepMerge.js

/*!
 * Deep merge two or more objects or arrays.
 * (c) 2023 Chris Ferdinandi, MIT License, https://gomakethings.com
 * @param   {*} ...objs  The arrays or objects to merge
 * @returns {*}          The merged arrays or objects
 */
function deepMerge (...objs) {

	/**
	 * Get the object type
	 * @param  {*}       obj The object
	 * @return {String}      The object type
	 */
	function getType (obj) {
		return Object.prototype.toString.call(obj).slice(8, -1).toLowerCase();
	}

	/**
	 * Deep merge two objects
	 * @return {Object}
	 */
	function mergeObj (clone, obj) {
		for (let [key, value] of Object.entries(obj)) {
			let type = getType(value);
			if (clone[key] !== undefined && getType(clone[key]) === type && ['array', 'object'].includes(type)) {
				clone[key] = deepMerge(clone[key], value);
			} else {
				clone[key] = structuredClone(value);
			}
		}
	}

	// Create a clone of the first item in the objs array
	let clone = structuredClone(objs.shift());

	// Loop through each item
	for (let obj of objs) {

		// Get the object type
		let type = getType(obj);

		// If the current item isn't the same type as the clone, replace it
		if (getType(clone) !== type) {
			clone = structuredClone(obj);
			continue;
		}

		// Otherwise, merge
		if (type === 'array') {
			clone = [...clone, ...structuredClone(obj)];
		} else if (type === 'object') {
			mergeObj(clone, obj);
		} else {
			clone = obj;
		}

	}

	return clone;

}