{"id":101463,"date":"2025-02-21T12:34:08","date_gmt":"2025-02-21T12:34:08","guid":{"rendered":"https:\/\/peraltafinancing.com\/analytics\/prevent-duplicate-transactions-in-google-analytics-with-customtask\/"},"modified":"2025-02-21T12:34:08","modified_gmt":"2025-02-21T12:34:08","slug":"prevent-duplicate-transactions-in-google-analytics-with-customtask","status":"publish","type":"post","link":"https:\/\/fivemor.com\/?p=101463","title":{"rendered":"Prevent Duplicate Transactions In Google Analytics With customTask"},"content":{"rendered":"


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One of the big problems in Google Analytics\u2019<\/a> data model is the immutability of historical data. Once a row of data is written into the data table, it is there practically for good. This is especially annoying in two cases: spam<\/a> and bogus ecommerce hits. The first is a recognized issue with an open and public data collection protocol<\/a>, the latter is an annoyance that can explode into full-blown sabotage (you can use the Measurement Protocol to send hundreds of huge transactions to your competitor\u2019s GA property, for example).<\/p>\n

In this article, I\u2019ll tackle a different symptom. I\u2019ve covered this before<\/a>, and David Vallejo\u2019s written an excellent article<\/a> about this topic as well.<\/p>\n

The problem is duplicate transactions<\/strong>. It\u2019s very common if your site has a receipt page that can be revisited via the browser cache or history. By revisiting the receipt page, it\u2019s often the case that the transaction details are written into dataLayer<\/code> (or sent with the ga()<\/code> method) again, resulting in the inflation of your ecommerce data.<\/p>\n

A simpler way to confirm if this is an issue is to create custom report<\/strong> where you inspect Transaction IDs against the Transactions metric. Optimally, you\u2019d have one transaction per ID, unless you\u2019ve decided to enable transaction updates\/upgrades in your data collection.<\/p>\n

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\"Duplicate<\/p>\n

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I\u2019ve decided to upgrade my solution to utilize customTask<\/a>, since it lets you do without extra triggers or variable logic. We\u2019ll set things up with Google Tag Manager<\/a>, but there\u2019s nothing stopping you from doing this with on-page analytics.js, too.<\/p>\n


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How it works<\/h2>\n

When you add the customTask<\/code> variable to your tags, it activates any time the tag tries to send a hit to Google Analytics.<\/p>\n

During this activation, the method looks for the key &ti<\/code> in the hit model. This key corresponds to the Transaction ID<\/strong><\/a> value.<\/p>\n

Next, it looks into your browser storage for any transaction IDs already sent from the current browser.<\/p>\n

If the transaction ID in the hit is found in browser storage, this customTask<\/code> blocks the hit from ever being fired, this preventing the duplicated information from reaching Google Analytics.<\/p>\n

If the transaction ID in the hit is not<\/strong> found in browser storage, the customTask<\/code> sends the hit to GA normally, but it also stores the transaction ID in the list of transactions that has already been recorded. Thus, it blocks any future<\/strong> hits with this ID from being sent.<\/p>\n

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\"deduplication<\/p>\n

<\/a><\/p>\n<\/div>\n

NOTE!<\/strong> This auto-blocking feature only works with Enhanced Ecommerce<\/a>. With Standard Ecommerce, the customTask<\/code> will only update browser storage but it won\u2019t block anything. You\u2019ll need to use triggers instead (read on for instructions how to do this).<\/p>\n

The customTask variable<\/h2>\n

You can use the customTask Builder tool<\/a> to generate the necessary variable, or you can simply copy-paste the code below into a Custom JavaScript variable<\/strong>, if you wish. The benefit of using the builder tool is that you can combine this customTask<\/code> with all the other setups I\u2019ve added to the tool.<\/p>\n

Anyway, this is what the Custom JavaScript variable should end up looking like:<\/p>\n

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function<\/span>() {\n  \/\/ customTask Builder by Simo Ahava\n<\/span>  \/\/\n<\/span>  \/\/ More information about customTask: https:\/\/www.simoahava.com\/analytics\/customtask-the-guide\/\n<\/span>  \/\/\n<\/span>  \/\/ Change the default values for the settings below.\n<\/span>\n  \/\/ transactionDeduper: Configuration object for preventing duplicate transactions from being recorded.\n<\/span>  \/\/ https:\/\/bit.ly\/2AvSZ2Y\n<\/span>  var<\/span> transactionDeduper = {\n    keyName: '_transaction_ids'<\/span>,\n    cookieExpiresDays: 365<\/span>\n  };\n\n  \/\/ DO NOT EDIT ANYTHING BELOW THIS LINE\n<\/span>  var<\/span> readFromStorage = function<\/span>(key) {\n    if<\/span> (!window<\/span>.Storage) {\n      \/\/ From: https:\/\/stackoverflow.com\/a\/15724300\/2367037\n<\/span>      var<\/span> value = '; '<\/span> + document<\/span>.cookie;\n      var<\/span> parts = value.split('; '<\/span> + key + '='<\/span>);\n      if<\/span> (parts.length === 2<\/span>) return<\/span> parts.pop().split(';'<\/span>).shift();\n    } else<\/span> {\n      return<\/span> window<\/span>.localStorage.getItem(key);\n    }\n  };\n\n  var<\/span> writeToStorage = function<\/span>(key, value, expireDays) {\n    if<\/span> (!window<\/span>.Storage) {\n      var<\/span> expiresDate = new<\/span> Date<\/span>();\n      expiresDate.setDate(expiresDate.getDate() + expireDays);\n      document<\/span>.cookie = key + '='<\/span> + value + ';expires='<\/span> + expiresDate.toUTCString();\n    } else<\/span> {\n      window<\/span>.localStorage.setItem(key, value);\n    }\n  };\n\n  var<\/span> globalSendHitTaskName   = '_ga_originalSendHitTask'<\/span>;\n\n  return<\/span> function<\/span>(customTaskModel) {\n\n    window<\/span>[globalSendHitTaskName] = window<\/span>[globalSendHitTaskName] || customTaskModel.get('sendHitTask'<\/span>);\n    var<\/span> tempFieldObject, dimensionIndex, count, ga, tracker, decorateTimer, decorateIframe, iframe;\n\n    customTaskModel.set('sendHitTask'<\/span>, function<\/span>(sendHitTaskModel) {\n\n      var<\/span> originalSendHitTaskModel = sendHitTaskModel,\n          originalSendHitTask      = window<\/span>[globalSendHitTaskName],\n          canSendHit               = true<\/span>;\n\n      var<\/span> hitPayload, hitPayloadParts, param, val, regexI, trackingId, snowplowVendor, snowplowVersion, snowplowPath, request, originalTrackingId, hitType, nonInteraction, d, transactionId, storedIds;\n\n      try<\/span> {\n\n        \/\/ transactionDeduper\n<\/span>        if<\/span> (typeof<\/span> transactionDeduper === 'object'<\/span> && transactionDeduper.hasOwnProperty('keyName'<\/span>) && transactionDeduper.hasOwnProperty('cookieExpiresDays'<\/span>) && typeof<\/span> sendHitTaskModel.get('&ti'<\/span>) !== 'undefined'<\/span>) {\n          transactionId = sendHitTaskModel.get('&ti'<\/span>);\n          storedIds = JSON.parse(readFromStorage(transactionDeduper.keyName) || '[]'<\/span>);\n          if<\/span> (storedIds.indexOf(transactionId) > -1<\/span> && ['transaction'<\/span>, 'item'<\/span>].indexOf(sendHitTaskModel.get('hitType'<\/span>)) === -1<\/span>) {\n            canSendHit = false<\/span>;\n          } else<\/span> if<\/span> (storedIds.indexOf(transactionId) === -1<\/span>) {\n            storedIds.push(transactionId);\n            writeToStorage(transactionDeduper.keyName, JSON.stringify(storedIds), transactionDeduper.cookieExpiresDays);\n          }\n        }\n        \/\/ \/transactionDeduper\n<\/span>\n        if<\/span> (canSendHit) {\n          originalSendHitTask(sendHitTaskModel);\n        }\n\n      } catch<\/span>(e) {\n        originalSendHitTask(originalSendHitTaskModel);\n      }\n\n    });\n\n  };\n}\n<\/code><\/pre>\n<\/div>\n
There\u2019s a configuration object in the variable transactionDeduper<\/code> that you can modify, if you wish. The configuration object must have both keyName<\/code> and cookieExpiresDays<\/code>.<\/p>\n
Set keyName<\/code> to what you want the name of the cookie or the localStorage<\/code> key to be. The default value is _transaction_ids<\/code>.<\/p>\n
Set cookieExpiresDays<\/code> to the number of days the cookie should exist. A cookie is only used if the user\u2019s browser doesn\u2019t support localStorage<\/code>. If localStorage<\/code> is used, no expiration is set.<\/p>\n
The main logic happens near the end of the code block, where I\u2019ve boxed the solution with \/\/ transactionDeduper<\/code> and \/\/ \/transactionDeduper <\/code>.<\/p>\n
It really is very simple, and it follows the process I outlined in the previous chapter.<\/p>\n
If you\u2019re using Enhanced Ecommerce<\/strong>, then this customTask<\/code> will take care of everything for you. In case the transaction ID is found in the list of stored IDs, it will simply block the hit from departing to Google Analytics.<\/p>\n
If you\u2019re using Standard Ecommerce<\/strong>, the customTask<\/code> will only write the ID into storage, and you\u2019ll need to handle the blocking logic yourself.<\/p>\n
Triggers and variables for Standard Ecommerce<\/h2>\n
Due to how Standard Ecommerce is split into transaction<\/code> and item<\/code> hits, the blocking logic would be extremely difficult to automate in customTask<\/code>. This is why you\u2019ll need to create an exception<\/strong> trigger for your Transaction tag, which blocks the tag from firing if the transaction ID is found in the list of stored IDs.<\/p>\n
Data Layer variable for the Transaction ID<\/h3>\n
Create a Data Layer variable<\/strong> for transactionId<\/code>, like this:<\/p>\n
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    <\/p>\n
    \"DLV<\/p>\n
    <\/a><\/p>\n<\/div>\n
In any case, you need to add this customTask<\/code> variable to all the Enhanced Ecommerce and\/or Transaction tags that have the power to send purchase information to Google Analytics. For instructions how to add the customTask<\/code> to your tags, see this guide<\/a> or follow the instructions in the customTask Builder tool<\/a>.<\/p>\n