Basic calculator, dynamic operator

by lasha

HTML

<input id="item1" type="text">

<select id="selectOperator">
    <option value="add">add</option>
    <option value="subtract">subtract</option>
    <option value="divide">divide</option>
</select>
    
<input id="item2" type="text"><br>
<button id="submitBtn">RESULT</button><br><br>
    
Result of math: <div class="math-result"></div>

JavaScript

(function(){
    var submitBtn = document.getElementById("submitBtn");
    var resultBox = document.querySelector(".math-result");
    var mathOperator;
    
    console.log(submitBtn, resultBox);
    
    var getKeys = function(obj){
        var keys = [];
        for(var key in obj){
            keys.push(key);
        }
        return keys;
    }
    
    function doTheMath(operator, value1, value2){
        var mathResult;
        value1 = parseInt(value1);
        value2 = parseInt(value2);
        
        switch(operator) {
            case 'add':
                console.log("add");
                mathResult = value1 + value2;
                break;
            case 'subtract':
                console.log("sub");
                mathResult = value1 - value2;
                break;
            case 'divide':
                console.log("divide");
                mathResult = value1 / value2;
                break;
            default:
                alert("please select operator");
        }
        
        return mathResult;
    }
    
    submitBtn.onclick = function(e){
        var value1 = document.getElementById("item1").value;
        var value2 = document.getElementById("item2").value;
        
        mathOperator = document.getElementById("selectOperator").value;
        
        resultBox.innerHTML = doTheMath(mathOperator, value1, value2);
    };
})();