JS – Deep Merge Test

deepMerge.js

/**
 * Deep merge test
 *
 * Performs a recursive Object.assign, copying properties from source to target
 * without removing any of the targets own properties
 *
 * @param   {object}  target  Target object, to copy properties to
 * @param   {object}  source  Source object, to copy proeprties from
 *
 * @return  {objuect}         Merged object
 */
function deepMerge(target, source)
{
	// Start with a clone of the target object
	// (copy target props to empty obj, then set the new merged var to that obj)
	let merged = Object.assign({}, target);

	// Loop through the properties of the source object,
	// to compare these props against the target's props
	for(const prop in source)
	{
		// Is property exclusive to source?
		if (!target.hasOwnProperty(prop))
		{
			// Exclusive source property: We can copy this over directly
			merged[prop] = source[prop];
		}
		else
		{
			// Shared property: Is it an object (so do we need to iterate over it?)
			if (typeof source[prop] !== 'object')
			{
				// Not an object, no iteration necessary, safe to copy!
				merged[prop] = source[prop];
			}
			else
			{
				// Shared property is an object, so iterate over its own properties
				// This starts the whole loop over again, at a deeper property level
				Object.assign(merged[prop], deepMerge(merged[prop], source[prop]));
			}
		}
	}

	return merged;
}