jasperkennis/replace.html

## replace.html
<!-- Place this just before the closing tag of <body> -->
<script>
  (function(){
    function getParams () {
      const paramsToReplace = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_content', 'utm_term'];
      const res = [];
      const windowParams = new URLSearchParams(window.location.search);
      for (let i = 0; i < paramsToReplace.length; i++) {
        const paramName = paramsToReplace[i];

        if (windowParams.has(paramName)) {
          res.push({
            name: paramName,
            value: windowParams.get(paramName)
          })
        }
      }

      return res;
    }

    function replaceValues (existingValues, replacementParams) {
      if (existingValues == null) {
        existingValues = '';
      }

      const existingParams = new URLSearchParams(existingValues);

      for (let i = 0; i < replacementParams.length; i++) {
        const replacementParam = replacementParams[i];
        existingParams.set(
          replacementParam.name,
          replacementParam.value
        )
      }

      return existingParams;
    }

    function prepareLinks() {
      const replacementParams = getParams();
      const links = document.getElementsByTagName('a');
      for (let i = 0; i < links.length; i++) {
        const thisLink = links[i];
        if (!thisLink.hasAttribute('href')) {
          continue;
        }
        const currentHrefParts = thisLink.getAttribute('href').split('?');
        currentHrefParts[1] = replaceValues(currentHrefParts[1], replacementParams);
        thisLink.setAttribute('href', currentHrefParts.join('?'))
      }
    }


    try {
      prepareLinks()
    } catch (error) {
      console.error('Failed to replace google tags.');
      console.error(error);
    }
  })()
</script>