[GTM] Get the item order in a list

Posted on | Edited on |

Google Tag Manager(GTM) is a back office for quickly managing HTML on webpages, basically, it enables the maintainer to do Everything on their website without changing the code base. There are three major elements in GTM which are Tag, Variable, and Trigger.

Tag

A Tag will be triggered by the Trigger you set and passing both the system defined variables and the user-defined variables to your Tag, then you could take the action such as sending it to GA or manipulate DOM on your pages.

Variable

Other than System defined variables, you could create your own by Javascript:
Select User-Defined Variables, then select the type Custom Javascript

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function() {
  try {
    var element = {{Click Element}}
    var elementClass = {{Element class}}
    if (!element || !elementClass) return
    var selector = '.' + elementClass.split(' ').join('.')
    var list = document.querySelectorAll(selector)
    var order = [].indexOf.call(list, element) + 1
    return order
  } catch (e) {
    if (window.dataLayer.filter(function (obj) {
      return obj.errorMsg === e.message;
    }).length == 0) {
      window.dataLayer.push({
        'event': 'variable error',
        'errorMsg': e.message
      });
    }
  }
}

Trigger