Call function on specific dropdown selection

Question

I am trying to call a simple function on a specific option selection in a dropdown menu.

In this example, I want to the function to execute only when the 4th option is selected

<select onchange="if (this.selectedIndex = 4) mypopup();">
<option value="1">P1</option>
<option value="2">P2</option>
<option selected="selected" value="3">P3</option>
<option value="4">P4</option>
</select>

Answer 1

It's very simple.

First you need to use this.value instead of this.selectedIndex.

Second thing is you must use == to test equality, instead of = to set a new value

let mypopup = function() {
  alert("Popup")
}

    <select onchange="if (this.value == 4) mypopup();">
      <option value="1">P1</option>
      <option value="2">P2</option>
      <option selected="selected" value="3">P3</option>
      <option value="4">P4</option>
    </select>