Change text if the value of the variable is undefined

I want to have it so that when the variable is undefined the text displays "variable is undefined" but my current code does not do this.

if (metar.clouds) {
        document.getElementById('cloud_block').classList.remove("d-none");
        metar.clouds.forEach(cloud => {
          var el = document.createElement('li');
          el.innerHTML = cloud.text + ' at ' + cloud.feet + 'ft AGL. ';
          document.getElementById("cloud_list").appendChild(el);
        });
      }

      if (typeof cloud.feet === "undefined") {
      cloud.feet = "variable is undefined";
    }