const paren = document.createElement('div');

let n = 0;

    const div = document.createElement('div');

    const p = document.createElement('p');

    p.classList.add('font-bold');

    p.textContent = 'Hello!';

    div.appendChild(p);

while(true) {

    n++;

    paren.appendChild(div.cloneNode(true));

    if(n===100000) 

        break;

}

​

const paren = document.createElement('div');

let n = 0;

let str= [];

while(true) {

    n++;

    str.push('<div><p class="font-bold">Hello!</p></div>');

    if(n===100000) 

        break;

}

paren.innerHTML = str.join('');