script.js

let display = document.getElementById('display');

let buttons = Array.from(document.getElementsByClassName('button'));

buttons.map(button => {
    button.addEventListener('click', (e) =>{
        switch(e.target.innerText){
            case 'C':
                display.innerText = '';
                break;
            case '←':
                if(display.innerText){
                    display.innerText = display.innerText.slice(0-1);
                } 
                break;
                case '=':
                    try{
                        display.innerText = eval(display.innerText);
                    } catch {
                        display.innerText ="ERROR";
                    }
                    break;
                default:
                    display.innerText += e.target.innerText;    
           }
    })
})