如果然后使用javascript

Question

我一直在玩这个剧本并且不能让它发挥作用。它总是默认为option3。

有人可以帮忙吗？

<select id="select">
  <option>Please select</option>
  <option value="option1">option1</option>
  <option value="option2">option2</option>
  <option value="option3">option3</option>
</select>
<div id="demo"></div>

<script>

document.getElementById("select").addEventListener("change", myFunction);

function myFunction() {
    if (document.getElementById("select").value = "option1") {
    option = "option 1 chosen";
    }
    if (document.getElementById("select").value = "option2") {
    option = "option 2 chosen";
    }
    if (document.getElementById("select").value = "option3") {
    option = "option 3 chosen";
    }
    document.getElementById("demo").innerHTML = option;
}

</script>

Answer 1

= assignment operator用于将值分配给符号左侧的变量。 == abstract equality operator或=== strict equality operator用于比较值。

function myFunction() {
  if(document.getElementById('select').value === 'option1') {
    option = 'option 1 choosen';
  }
  if(document.getElementById('select').value === 'option2') {
    option = 'option 2 choosen';
  }
  if(document.getElementById('select').value === 'option3') {
    option = 'option 3 choosen';
  }
  document.getElementById("demo").innerHTML = option;
}