If you have ever needed to dynamically fill in a HubSpot Form field, this is code for you.

dynamic-fill-in-hubspot-forms-once-ready.js

<script>
  //Only need to process each form once it's ready.
  let processed = {};
  
  //Loop over the event listener and look only for hsFormCallback and onFormReady
  window.addEventListener('message', function(event) {
    if(event.data.type === 'hsFormCallback' && event.data.eventName === 'onFormReady') {
      const forms = event.currentTarget.HubSpotForms.getForms();
      forms.forEach(form=>{
        //Checking if it's ready.
        if( form.isFormReady ) {
          fillInFields(form.id + '_' + form.instanceId);
        }
      });
    }
  });
  
  /**
   * Fills in the Fields within each specific form that is passed in
   * @param string
   *  EX: 3fadb772-36ff-40b2-a830-043cf24a26e2_89602285-47f9-44ab-b255-3d4419d767d1
   */
  function fillInFields(form) {
    if( processed[form] ) {
      return;
    }
    let element = document.querySelector('form.hs-form-'+form);
    if( element ) {
      //Add in any inputs, selects, etc.. here
      let input = element.querySelector('input[name="case_study___requested_download"]');
      if( input ) {
        input.value = '{{row.name}}';
      }
      processed[form] = true;
    }
  }
</script>