js-calculator/main.js

const dis_big = document.getElementById("dis_big");
const dis_sml = document.getElementById("dis_sml");

const calc = new Calculator();

const buttons = document.querySelector('.buttons');
buttons.addEventListener('click', e => {
    const value = e.target.value;
    PressButton(value);
})

function PressButton(button) {
    calc.pressbutton(button);

    tmp = '';
    switch (calc.operator) {
        case 'ADD':
            tmp = ' +';
            break;
        case 'SUB':
            tmp = ' -';
            break;
        case 'MUL':
            tmp = ' *';
            break;
        case 'DIV':
            tmp = ' /';
            break;
        default:
            console.log('Invalid operator');
            break;
    }

    dis_big.innerText = calc.curr;
    dis_sml.innerText = calc.prew + tmp;
}