如何将此代码从 Jquery 转换为 Vanilla Javascript？

Question

I need to translate this code from Jquery to Vanilla JS. I provide you all code but only is an important JS file. HTML and scss files not important, maybe only for catching class and nodes. I will provide and codepen code: https://codepen.io/lakialex/pen/eqvEBR . For all question i am here

HTML:

<div class="dropdown">
    <button class="dropbtn dropbtn-three">
        DropDown Parent
        <i class="fa fa-angle-down"></i>
    </button>
    <div class="dropdown-content">
        <ul>
            <li class="item-has-children">
                <a href="#0" class="padd-left">List 1 <span class="rightt">  </span></a>
                <ul class="sub-menu">
                    <li><a href="#0">List 2 sub menu <span class="rightt">  </span></a>
                        <ul class="sub-menu">
                            <li><a href="Dropdown3/Wahlergebnisse-der-Landtagswahl-2017/Zielsetzungen/entwicklung-zu-einem-souveränen-staat.html">List 3 sub menu </a></li>
                            <div class="hr2"></div>
                            <li><a href="Dropdown3/Wahlergebnisse-der-Landtagswahl-2017/Zielsetzungen/verpflichtung-zu-internationaler-solidarität.html">List 3 sub menu </a></li>
                        </ul>
                    </li>
                </ul>
            </li>
        </ul>
    </div>
</div>

SCSS:

$facebookBlue: #153161;
$strongRed: #9a0000;
$strongYellow: #000;
$white: #ffffff;
 * {
    box-sizing: border-box;
}
body {
  display: flex;
  padding-top: 40px;
}
.dropdown {
    position: relative;
    display: inline-block;
  margin: 0 auto;
    .dropbtn {
        background-color: $facebookBlue;
        color: $white;
        font-size: 17px;
        font-weight: 600;
        border: none;
        cursor: pointer;
        height: 55px;
        background: #153161;
        border-bottom-left-radius: 7px;
        border-bottom-right-radius: 7px;
        padding: 12px 50px;
        position: relative;
        width: 360px;
        text-align: left;
        i {
            margin-left: 30px;
            color: #8391ab;
            // opacity: 0.2;
            position: absolute;
            top: 50%;
            right: 25px;
            transform: translateY(-50%);
        }
        .arrow {
            width: 0;
            height: 0;
            border-left: 10px solid transparent;
            border-right: 10px solid transparent;
            border-top: 10px solid #8191aa;
            margin: 100%;
            padding-top: 4px;
            z-index: 999;
        }
    }
    .dropbtn-two {
        background: $strongRed;
    }
    .dropbtn-three {
        background: $strongYellow;
    }
}

.dropdown-content {
    display: none;
    position: absolute;
    background-color: #f9f9f9;
    min-width: 160px;
    box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
    width: 330px;
    z-index: 999;
    a {
        color: black;
        padding: 12px 25px;
        text-decoration: none;
        display: flex;
        justify-content: flex-start;
        width: 100%;
        &:hover {
            background-color: #F8F8F8
        }
    .rightt {
      display: inline-block;
      // width: 9px;
      // height: 9px;
      cursor: pointer;
      // padding-left: 180px;
      position: absolute;
      right: 20px;
      top: 50%;
      transform: translateY(-50%);
      z-index: 999;
      &:after {
        content: '';
        display: inline-block;
        width: 9px;
        height: 9px;
        border-top: 0.2em solid #ababab;
        border-right: 0.2em solid #ababab;
        -moz-transform: rotate(45deg);
        -webkit-transform: rotate(45deg);
        transform: rotate(45deg);
      }
    }
    &.selected {
      padding-left: 70px;
      .rightt {
        left: 40px;
        top: 25%;
        right: auto;
        transform: translateY(0);
        transform: rotate(180deg);
      }
    }
    }

    .left {
        display: inline-block;
        cursor: pointer;
        position: absolute;
        right: 20px;
        top: 50%;
        transform: translateY(-50%);
        z-index: 999;
        &:after {
            content: '';
            display: inline-block;
            width: 29px;
            height: 29px;
            border-top: 0.2em solid #ababab;
            border-right: 0.2em solid #ababab;
            -moz-transform: rotate(45deg);
            -webkit-transform: rotate(45deg);
            transform: rotate(45deg);
        }
    }
    .item-has-children {
        a {
            position: relative;
        }
    }
}

.dropdown:hover .dropdown-content {
    display: block;
    background: white;
    opacity: 0.95;
    width: 100%;
}

.hr2 {
    height: 1px;
    background: #ccc;
    border-bottom: 1px solid #fff;
    border-top: 1px solid #ccc;
}

.sub-menu {
    display: none;
}

.sub-menu.selected {
    display: flex;
    flex-direction: column;
    transition: transform 0.6s;
}

ul {
    list-style: none;
    padding: 0 0px;
    width: 100%;
    height: 100%;
}

JS:

const links = $('.item-has-children a');

links.each(function() {
    $(this).on('click', function() {
      if ($(this).hasClass('selected')) {
        $(this).parent().parent().prev().show();
        $(this).next('ul').hide();
        $(this).removeClass('selected');
      } else {
        $(this).parent().parent().prev().hide();
        $(this).next('ul').show();
        $(this).addClass('selected');
      }
    });
});

Answer 1

This should do the trick

document.querySelectorAll(".item-has-children a").forEach(element => {
    element.addEventListener('click', () => {
        if (element.classList.contains('selected')) {
            const parentsibling = element.parentElement.parentElement.previousElementSibling;
            if (parentsibling) parentsibling.style.display = 'block';
            let nextSibling = element;
            while (nextSibling !== null && nextSibling.nodeName !== 'UL') {
                nextSibling = nextSibling.nextElementSibling;
            }
            if (nextSibling) nextSibling.style.display = 'none';
            element.classList.remove('selected');
        } else {
            const parentsibling = element.parentElement.parentElement.previousElementSibling;
            if (parentsibling) parentsibling.style.display = 'none';
            let nextSibling = element;
            while (nextSibling !== null && nextSibling.nodeName !== 'UL') {
                nextSibling = nextSibling.nextElementSibling;
            }
            if(nextSibling) nextSibling.style.display = 'block';
            element.classList.add('selected')
        }
    })
})

However, as other have stated in comments, you should probably learn to search for this on your own. You can find more informations on the methods I used to do this here :

querySelectorAll

parentNode

addEventListener

previousElementSibling

nextElementSibling

classList

You can also find all of jQuery source code on GitHub, which might help you understand how they do things comprehensively !