How do you use an if statement to extract a value from a select tag? (Javascript)

Question

My first input box

<input type="number" id="number1">
<br>
<br>

My options

<input type="number" id="number1">
<select id="operation">  
<option value="add">Add</option>
<option value="subtract">Subtract</option>
</select>
<br>
<br>

My second input box

<input type="number" id="number2">
<br>
<br>

This is a button below

<button onclick="calculateNum()">Calculate</button>
<br>
<p id="result">This is your result....</p>
</select>
<script>
function calculateNum(){
var operation = document.getElementById("operation").value;

In the below code (if statements), do I have syntax errors of any kind?

if(operation == "add"){
var num1 = document.getElementById("num1");
var num2 = document.getElementById("num2");
var result = parseInt(number1) + parseInt(number2);
document.getElementById("result").innerHTML = result;
}
else if(operation == "subtract"){
var num1 = document.getElementById("num1");
var num2 = document.getElementById("num2");
var result = parseInt(number1) - parseInt(number2);
document.getElementById("result").innerHTML = result;
}
}
</script>

Answer 1

Try getting the index of selected option and selecting it from options like so:

let selectField = document.getElementById('operation');
let operation = selectField.options[selectField.selectedIndex].value;
if (operation == "add") {
    // do something
}