🟦 UNDO기능

🔹memento형식

https://stackoverflow.com/questions/54416318/how-to-make-a-undo-redo-function

const mementos = []
const input = document.querySelector('input')

function saveMemento() {
  mementos.push(input.value)
}

function undo() {
  const lastMemento = mementos.pop()
   
  input.value = lastMemento ? lastMemento : input.value
}
<h4> Type some characters and hit Undo </h4>
<input onkeydown="saveMemento()" value="Hello World"/>
<button onclick="undo()">Undo</button>

🔹 js 배열의 push() , pop()함수

• push : 배열의 끝에 아이템을 추가한다.
• pop : 배열의 마지막 아이템을 제거한다.

🔹 elem.classList.add()

🔹 elem.append() + elem.lastElementChild.remove()

    addEvent : function (elem) {
        const imgElem = elem.firstElementChild;
        elem.addEventListener('mouseover', () => {
            imgElem.classList.add('blurImg');
            this.showIcn(elem);
        });
        elem.addEventListener('mouseout', () => {
            imgElem.classList.remove('blurImg');
            this.hideIcn(elem);
        });
    },
    showIcn : function (elem) {
        const favIcn = this.favIcn(elem.dataset.isfav);
        const cmtIcn = this.cmtIcn(elem.dataset.iscmt);

        const icnElem = document.createElement('div');
        icnElem.id = 'icn';
        icnElem.append(favIcn);
        icnElem.append(cmtIcn);
        icnElem.style.position = 'absolute';

        elem.append(icnElem);
    },
    hideIcn : function (elem) {
        if(elem.childElementCount>1) {
            elem.lastElementChild.remove();
        }
    }