Google Tag Manager

How to flatten the GTM dataLayer

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Unlike Adobe Launch or Tealium, the Google Tag Manager uses a nested dataLayer Object to structure its content. Since I kinda “grow up” with GTM, I am totally used to that. But recently I had within a client project a use case where I preferred to use a flat dataLayer.

A flat dataLayer can esp. help you with custom JavaScripts while not using GTM variables. The GTM variables are already working as a flat dataLayer object anyway.

The following code snippet will make the dataLayer flat.

Important: duplicate keys will be overwritten with the latest one. This is actually the key feature here, but important to know and understand.

function flat_dataLayer(ob)
	var toReturn = {};
	for (var i in ob) {
		if (!ob.hasOwnProperty(i)) continue;

		if ((typeof ob[i]) == 'object') {
			var flatObject = flat_dataLayer(ob[i]);
			for (var x in flatObject) {
				if (!flatObject.hasOwnProperty(x)) continue;

				toReturn[x] = flatObject[x];
		} else {
			toReturn[i] = ob[i];
	return toReturn;

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