JS Calculator showing wrong output

I have build a calculator and it shows following calculation wrong.
Capture

here is my calculate function

function calculate(firstNumber,operator,secondNumber){
    let first=parseFloat(firstNumber);
    let second=parseFloat(secondNumber);
    switch(operator){
        case 'add': return first + second;
        case 'minus': return first - second; 
        case 'multiply': return first * second; 
        case 'divide': return first / second;
    }
}

it’s actually correct, if you want to avoid that you will need to work out the workaround

see this video