git/calc.html at master · chldPDms/git · GitHub

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<body>
    <input type="text" id="num1"/>

    <select id="operations">
        <option>+</option>
        <option>-</option>
        <option>*</option>
        <option>/</option>
    </select>

    <input type="text" id="num2"/>
    <input type="button" id="btn" value="계산"/>
    <div id="result"></div>
</body>

<script>
    let num1 = document.querySelector("#num1")
    let num2 = document.querySelector("#num2")
    let btn = document.querySelector("#btn")
    let result = document.querySelector("#result")
    let operations = document.querySelector("#operations")

    btn.addEventListener("click", function(){
        let a = parseInt(num1.value);
        let b = parseInt(num2.value);
        let r;
        switch(operations.value){
            case "+": r = a+b;
            break;
            case "-": r = a-b;
            break;
            case "*": r = a*b;
            break;
            case "/": r = a/b;
            break;

        }
        result.innerText = r
    });

</script>