如果变量的值未定义，则更改文本

Question

我想要它，以便当变量未定义时，文本显示“变量未定义”，但我当前的代码不会这样做。

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";
    }

Answer 1

不应该是这样的代码

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

如果变量的值未定义，则更改文本

Change text if the value of the variable is undefined

javascript

if-statement

undefined