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Metodo ClassList.contains
Fantastico! Abbiamo creato un contatore di Mi piace che aumenta di valore a ogni clic. Ma il numero di like non dovrebbe semplicemente aumentare.
Se all'utente non è ancora piaciuto, cliccando sul "cuore" il contatore aumenta. Se invece l'utente ha già ricevuto un "mi piace", il clic sul "cuore" dovrebbe far diminuire il contatore. Come distinguere questi clic?
Possiamo verificare se l'elemento heart ha una classe added. Se l'elemento non ha ancora la classe, verrà aggiunta; se invece ce l'ha già, verrà rimossa.
Per verificare se un elemento ha una classe, si utilizza il metodo classList.contains:
element.classList.contains('class');La classe da controllare è specificata tra parentesi. Il metodo classList.contains restituisce true se l'elemento ha una classe e false se non ce l'ha.
I valori true e false sono chiamati valori booleani.
Vediamo come funziona il metodo classList.contains: diciamo a JavaScript di inviare alla console i valori restituiti da questo metodo e facciamo clic alcune volte sul "cuore" per attivare la classe.
Todos los archivos
<!DOCTYPE html>
<html lang="it">
<head>
<meta charset="utf-8">
<link rel="stylesheet" href="setting.css">
<link rel="stylesheet" href="style.css">
<title>FlashNews!</title>
</head>
<body class="page light-theme">
<header class="page-header">
<div class="container">
<span class="header-logo">
<img src="img/main-logo.svg" width="67" height="29" alt="FlashNews!">
</span>
<button class="theme-button" type="button">Cambia tema</button>
</div>
</header>
<main class="inner-news">
<article class="container">
<h1 class="inner-heading">🔥 Shock! Scandalo! Sensazione!</h1>
<div class="news-full">
<img src="img/news-robot2.jpg" alt="">
<div class="news-stats">
<button class="heart" type="button"><span class="likes-number"></span></button>
<time datetime="2019-12-22">22 dicembre 2019</time>.
</div>
<p>È emerso che non è necessario essere un gatto per iniziare a programmare in JavaScript! Gli scienziati hanno creato il primo robot in grado di evolversi e cambiare il proprio codice. Ha imparato subito a impaginare siti web e ha iniziato a lavorare come freelance a Bali.</p>
</div>
</article>
</main>
<footer class="page-footer">
<div class="container">
<p>© FlashNews!</p>
<span class="footer-logo">
<img src="img/white-logo.svg" alt="FlashNews!">
</span>
</div>
</footer>
<script src="themes.js"></script>
<script src="likes.js"></script>
</body>
</html>
/* стили страницы новости */
.comment-form {
display: flex;
margin-bottom: 30px;
padding: 20px 12px;
}
.comment-inner {
position: relative;
flex-grow: 1;
margin-right: 10px;
}
.comment-label {
position: absolute;
top: -16px;
left: -9px;
padding: 4px 8px;
font-size: 10px;
line-height: 14px;
}
.comment-field {
width: 100%;
height: 30px;
padding: 0 10px;
border: none;
background-color: transparent;
font: inherit;
font-size: 14px;
line-height: 30px;
}
.comment-field::placeholder {
color: #aaaaaa;
font: inherit;
font-size: 14px;
font-style: italic;
}
.comment-field:focus::placeholder {
font-size: 0;
}
.comment-field:hover::placeholder,
.comment-field:active::placeholder {
opacity: 0.5;
}
.inner-news .inner-heading {
margin-bottom: 20px;
font-size: 24px;
}
.news-full {
display: flex;
flex-direction: column;
margin-bottom: 24px;
}
.news-full img {
margin-bottom: 4px;
width: 100%;
height: 220px;
object-fit: cover;
}
.news-full .news-stats {
display: flex;
justify-content: space-between;
}
.news-full .heart {
padding: 12px 10px;
min-width: 40px;
min-height: 34px;
font-family: inherit;
font-weight: bold;
font-size: 16px;
border: none;
background-color: transparent;
background-repeat: no-repeat;
background-position: 12px;
cursor: pointer;
}
.heart .likes-number {
margin-left: 24px;
line-height: 14px;
}
.news-full time {
margin-top: 14px;
margin-right: 12px;
margin-bottom: 8px;
margin-left: 0;
}
.news-full p {
margin-top: 0;
margin-right: 12px;
margin-bottom: 16px;
margin-left: 12px;
font-size: 14px;
line-height: 24px;
}
.comment-feed h2 {
margin-top: 0;
margin-bottom: 12px;
}
.comment-list {
margin-top: 0;
margin-right: 0;
margin-bottom: 12px;
margin-left: 0;
padding: 0;
list-style: none;
counter-reset: comments;
}
.comment-list li {
margin-bottom: 6px;
padding: 10px 12px;
min-height: 36px;
font-size: 14px;
line-height: 24px;
}
.comment-list .user-comment {
position: relative;
display: flex;
}
.comment-list .user-comment::before {
counter-increment: comments;
content: "#" counter(comments);
padding-right: 12px;
margin-right: 12px;
border-right: 1px solid;
font-weight: bold;
}
.comment-list .user-comment::after {
position: absolute;
content: "";
width: 0;
height: 0;
bottom: 0;
left: -8px;
border: 4px solid;
border-left-color: transparent;
border-top-color: transparent;
}
@keyframes comment-blink-light {
0% {
background-color: #b6aaff;
opacity: 0;
}
20% {
opacity: 0.8;
}
}
@keyframes comment-blink-light-after {
0% {
border-right-color: #b6aaff;
border-bottom-color: #b6aaff;
opacity: 0;
}
20% {
opacity: 0.8;
}
}
@keyframes comment-blink-dark {
0% {
background-color: #473c8d;
opacity: 0;
}
20% {
opacity: 1;
}
}
@keyframes comment-blink-dark-after {
0% {
border-right-color: #473c8d;
border-bottom-color: #473c8d;
opacity: 0;
}
20% {
opacity: 1;
}
}
/* темы */
.dark-theme .header-logo {
filter: invert(1) hue-rotate(180deg) brightness(2);
}
/* Светлая тема */
.light-theme {
color: #333333;
background-color: #eae9f2;
}
.light-theme .page-header {
background-color: #ffffff;
box-shadow: 0 2px 2px rgba(0, 0, 0, 0.2);
}
.light-theme .header-link {
color: #6653d9;
}
.light-theme .header-link::before {
background-image: url("img/arrow-back-light.svg");
background-repeat: no-repeat;
background-position: 0 0;
}
.light-theme .theme-button {
color: #6653d9;
border: 1px solid #6653d9;
}
.light-theme .theme-button::before {
background-image: url("img/moon-normal.svg");
}
.light-theme .theme-button:focus,
.light-theme .theme-button:hover {
color: #ffffff;
background-color: #6653d9;
}
.light-theme .theme-button:focus {
outline-color: #b6aaff;
}
.light-theme .theme-button:focus::before,
.light-theme .theme-button:hover::before {
background-image: url("img/moon-hover.svg");
}
.light-theme .menu-open {
background-color: #ffffff;
background-image: url("img/menu-open-light.svg");
}
.light-theme .menu:focus {
outline-color: #b6aaff;
}
.light-theme .menu-open:focus,
.light-theme .menu-open:hover {
background-color: #6653d9;
background-image: url("img/menu-open-dark.svg");
}
.light-theme .menu-close {
background-color: #6653d9;
}
.light-theme .menu-close:focus,
.light-theme .menu-close:hover {
background-color: #473c8d;
}
.light-theme .main-menu {
background-color: #6653d9;
color: #ffffff;
}
.light-theme .main-menu a:focus,
.light-theme .main-menu a:hover {
background-color: #473c8d;
}
.light-theme .main-menu a:focus {
outline-color: #b6aaff;
}
.light-theme .news-view button {
border: 1px solid #6653d9;
color: #6653d9;
}
.light-theme .news-view button:focus,
.light-theme .news-view button:hover,
.light-theme .news-view button:active,
.light-theme .news-view .view-checked {
background-color: #6653d9;
color: #ffffff;
}
.light-theme .news-view button:focus {
outline-color: #b6aaff;
}
.light-theme .news-view .row-view:focus::before,
.light-theme .news-view .row-view:hover::before,
.light-theme .news-view .row-view:active::before {
background-image: url("img/rows-light-checked.svg");
}
.light-theme .news-view .tile-view:focus::before,
.light-theme .news-view .tile-view:hover::before,
.light-theme .news-view .tile-view:active::before {
background-image: url("img/tiles-light-checked.svg");
}
.light-theme .row-view::before {
background-image: url("img/rows-light.svg");
}
.light-theme .tile-view::before {
background-image: url("img/tiles-light.svg");
}
.light-theme .row-view.view-checked::before {
background-image: url("img/rows-light-checked.svg");
}
.light-theme .tile-view.view-checked::before {
background-image: url("img/tiles-light-checked.svg");
}
.light-theme .new-block {
background-color: #ffffff;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2);
}
.light-theme .news-full {
background-color: #ffffff;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2);
}
.light-theme .new-block time {
color: #aaaaaa;
}
.light-theme .news-full time {
color: #aaaaaa;
}
.light-theme .cookies-agreement {
background-color: #fdeacd;
box-shadow: 0 -1px 4px rgba(0, 0, 0, 0.2);
}
.light-theme .button {
background-color: #6653d9;
color: #ffffff;
}
.light-theme .button:focus,
.light-theme .button:hover {
background-color: #473c8d;
}
.light-theme .button:focus {
outline-color: #b6aaff;
}
.light-theme .page-footer {
background-color: #6653d9;
color: #ffffff;
}
.light-theme .subscription,
.light-theme .comment-form {
background-color: #ffffff;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.2);
}
.light-theme .subscription-message {
background-color: #6653d9;
color: #eae9f2;
}
.light-theme .subscription-message::before {
background-image: url("img/icon-ok-light.svg");
}
.light-theme .subscription-label,
.light-theme .comment-label {
color: #6653d9;
}
.light-theme .subscription-email,
.light-theme .comment-field {
border: 1px solid #eae9f2;
color: #333333;
}
.light-theme .heart {
color: #6653d9;
background-image: url("img/icon-heart-light.svg");
opacity: 0.7;
}
.light-theme .heart.added {
background-image: url("img/icon-heart-light-added.svg");
}
.page .heart:focus,
.page .heart:hover {
opacity: 1;
}
.light-theme .heart:focus {
outline-color: #b6aaff;
}
.light-theme .heart:active {
opacity: 1;
background-image: url("img/icon-heart-light-active.svg");
}
.light-theme .comment-list li {
background-color: #ffffff;
}
.light-theme .user-comment:not(:first-child) {
animation: comment-blink-light 600ms ease-in;
}
.light-theme .user-comment::before {
border-right-color: #eae9f2;
color: #cdcdcd;
}
.light-theme .user-comment::after {
border-right-color: #ffffff;
border-bottom-color: #ffffff;
}
.light-theme .user-comment:not(:first-child)::after {
animation: comment-blink-light-after 600ms ease-in;
}
.light-theme .comment-label {
background-color: #ffffff;
}
.light-theme .comment-field:focus {
outline-color: #b6aaff;
}
/* Тёмная тема */
.dark-theme {
color: #f2f2f2;
background-color: #17161a;
}
.dark-theme .page-header {
background-color: #373540;
box-shadow: 0 2px 2px rgba(0, 0, 0, 0.6);
}
.dark-theme .header-link {
color: #9484f2;
}
.dark-theme .header-link::before {
background-image: url("img/arrow-back-dark.svg");
background-repeat: no-repeat;
background-position: 0 0;
}
.dark-theme .theme-button {
color: #9484f2;
border: 1px solid #9484f2;
}
.dark-theme .theme-button::before {
background-image: url("img/sun-normal.svg");
}
.dark-theme .theme-button:focus,
.dark-theme .theme-button:hover {
color: #17161a;
background-color: #9484f2;
}
.dark-theme .theme-button:focus {
outline-color: #6653d9;
}
.dark-theme .theme-button:focus::before,
.dark-theme .theme-button:hover::before {
background-image: url("img/sun-hover.svg");
}
.dark-theme .menu:focus {
outline-color: #6653d9;
}
.dark-theme .menu-open {
background-color: #373540;
background-image: url("img/menu-open-dark.svg");
}
.dark-theme .menu-open:focus,
.dark-theme .menu-open:hover {
background-color: #473c8d;
background-image: url("img/menu-open-dark.svg");
}
.dark-theme .menu-close {
background-color: #473c8d;
}
.dark-theme .menu-close:focus,
.dark-theme .menu-close:hover {
background-color: #6653d9;
}
.dark-theme .main-menu {
background-color: #473c8d;
color: #f2f2f2;
}
.dark-theme .main-menu a:focus {
outline-color: #6653d9;
}
.dark-theme .main-menu a:focus,
.dark-theme .main-menu a:hover {
background-color: #6653d9;
}
.dark-theme .news-view button {
border: 1px solid #9484f2;
color: #9484f2;
}
.dark-theme .news-view button:focus {
outline-color: #6653d9;
}
.dark-theme .news-view button:focus,
.dark-theme .news-view button:hover,
.dark-theme .news-view button:active,
.dark-theme .news-view .view-checked {
background-color: #9484f2;
color: #17161a;
}
.dark-theme .news-view .row-view:focus::before,
.dark-theme .news-view .row-view:hover::before,
.dark-theme .news-view .row-view:active::before {
background-image: url("img/rows-dark-checked.svg");
}
.dark-theme .news-view .tile-view:focus::before,
.dark-theme .news-view .tile-view:hover::before,
.dark-theme .news-view .tile-view:active::before {
background-image: url("img/tiles-dark-checked.svg");
}
.dark-theme .row-view::before {
background-image: url("img/rows-dark.svg");
}
.dark-theme .tile-view::before {
background-image: url("img/tiles-dark.svg");
}
.dark-theme .row-view.view-checked::before {
background-image: url("img/rows-dark-checked.svg");
}
.dark-theme .tile-view.view-checked::before {
background-image: url("img/tiles-dark-checked.svg");
}
.dark-theme .new-block {
background-color: #2a2930;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.6);
}
.dark-theme .news-full {
background-color: #2a2930;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.6);
}
.dark-theme .new-block time {
color: #888888;
}
.dark-theme .news-full time {
color: #888888;
}
.dark-theme .cookies-agreement {
background-color: #473c8d;
box-shadow: 0 -1px 4px rgba(0, 0, 0, 0.6);
}
.dark-theme .button {
background-color: #9484f2;
color: #17161a;
}
.dark-theme .button:focus {
outline-color: #6653d9;
}
.dark-theme .button:focus,
.dark-theme .button:hover {
background-color: #b6aaff;
}
.dark-theme .page-footer {
background-color: #0a0910;
color: #f2f2f2;
}
.dark-theme .subscription,
.dark-theme .comment-form {
background-color: #2a2930;
box-shadow: 0 1px 4px rgba(0, 0, 0, 0.6);
}
.dark-theme .subscription-message {
background-color: #9484f2;
color: #17161a;
}
.dark-theme .subscription-message::before {
background-image: url("img/icon-ok-dark.svg");
}
.dark-theme .subscription-label,
.dark-theme .comment-label {
color: #9484f2;
}
.dark-theme .comment-label {
background-color: #2a2930;
}
.dark-theme .subscription-email,
.dark-theme .comment-field {
border: 1px solid #473c8d;
color: #f2f2f2;
}
.dark-theme .heart {
color: #9484f2;
background-image: url("img/icon-heart-dark.svg");
opacity: 0.7;
}
.dark-theme .heart:focus {
outline-color: #6653d9;
}
.dark-theme .heart.added {
background-image: url("img/icon-heart-dark-added.svg");
}
.dark-theme .heart:active {
opacity: 1;
background-image: url("img/icon-heart-dark-active.svg");
}
.dark-theme .comment-list li {
background-color: #2a2930;
}
.dark-theme .user-comment:not(:first-child) {
animation: comment-blink-dark 600ms ease-in;
}
.dark-theme .user-comment::before {
border-right-color: #17161a;
color: rgba(255, 255, 255, 0.3);
}
.dark-theme .user-comment::after {
border-right-color: #2a2930;
border-bottom-color: #2a2930;
}
.dark-theme .user-comment:not(:first-child)::after {
animation: comment-blink-dark-after 600ms ease-in;
}
.dark-theme .comment-field:focus {
outline-color: #6653d9;
}
let heart = document.querySelector('.heart');
let likesNumber = document.querySelector('.likes-number');
let counter = 0;
heart.onclick = function () {
// Aggiungere il codice qui
counter++;
likesNumber.textContent = counter;
heart.classList.toggle('added');
};
let page = document.querySelector('.page');
let themeButton = document.querySelector('.theme-button');
themeButton.onclick = function () {
page.classList.toggle('light-theme');
page.classList.toggle('dark-theme');
};
Il codice è cambiato, fai clic su "Aggiorna" o attiva l'esecuzione automatica.
Sei passato a un'altra pagina
Fare clic all'interno del mini-browser per evidenziare questa finestra.
100%
Consola
- Alla riga 6, scrivere l'istruzione
console.log(heart.classList.contains('added'));. - Fare clic sul "cuore".
- Aprire la console. Al momento del clic, la classe
addeddell'elemento non esisteva ancora, quindi l'output èfalse. - Fare nuovamente clic sul "cuore".
- Aprire la console. Al momento del clic, la classe
addeddell'elemento era presente, quindi l'output ètrue.