[MC-XOBAHCK]

Если так:

const parentsOfAllElements = document.body;

const divCalculator = document.createElement('div');
divCalculator.className = 'calculator-grid';
parentsOfAllElements.appendChild(divCalculator);

const divOutput = document.createElement('div');
divOutput.className = 'output';
divCalculator.appendChild(divOutput);

const btns = ['AC', 'DEL', '÷', 1, 2, 3, '*', 4, 5, 6, '+', 7, 8, 9, '-', '.', 0, '='];

for (let i = 0; i < btns.length; i++) {
    let btn = document.createElement('button');

    btn.innerText = btns[i];

    if (typeof btns[i] == 'number') {
        btn.setAttribute('data-number', '');
    }
    else if (btns[i].length == 1) {
        btn.setAttribute('data-operation', '');
    }
    else if (btns[i] == 'AC') {
        btn.setAttribute('data-all-clear', ''); 
        btn.className = 'span-two';
    }
    else if (btns[i] == 'DEL') {
        btn.setAttribute('data-delete', '');
    }

    divCalculator.appendChild(btn);
}