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What are you planning to do?</a></li><li class="main-nav__course-contents-item main-nav__course-contents-item--current"><a href="/courses/javascript-browser/dom/change-event">2. The “change” event</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/change-event-2">3. How the “change” event works</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/delete-element">4. Deleting the element from the list</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/check-collection-length">5. How to check the collection length</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/debug-code">6. Debugging the code</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/static-live-collection">7. Static and live collections</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/display-message">8. Displaying the message on the page</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/submit-event">9. The “submit” event</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/cancel-form-submit">10. Cancelling the form submission</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/obtain-text-input">11. How to obtain text from the input field</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/template-tag">12. Templates and the <template> tag</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/document-fragment">13. The contents of the <template> tag, document-fragment</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/clone-element">14. Cloning and inserting elements, part 1</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/clone-element-2">15. Cloning and inserting elements, part 2</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/clone-element-3">16. Cloning and inserting elements, part 3</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/clone-element-4">17. Cloning and inserting elements, part 4</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/clone-element-5">18. How to clone elements</a></li><li class="main-nav__course-contents-item"><a href="/courses/javascript-browser/dom/add-new-element">19. 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The third program: “Instant messenger”</a></li></ul></div></div><a class="main-nav__course-item main-nav__course-button main-nav__course-button--next" href="/courses/javascript-browser/dom/change-event-2">How the “change” event works</a></div><ul class="main-nav__list main-nav__list--user main-nav__list--user-guest"><li class="main-nav__item" itemprop="name"><a class="main-nav__link" href="/signup?redirect_url=%2Fcourses%2Fjavascript-browser%2Fdom%2Fchange-event" title="Sign up" data-modal="open" data-value="register" itemprop="url"><span class="main-nav__icon" aria-hidden="true"><svg aria-hidden="true"><use xlink:href="/img/sprites/general.svg#user"></use></svg></span>Sign up</a></li><li class="main-nav__item main-nav__item--login" itemprop="name"><a class="main-nav__link" href="/login?redirect_url=%2Fcourses%2Fjavascript-browser%2Fdom%2Fchange-event" title="Log in" data-modal="open" data-value="login" itemprop="url"><span class="main-nav__icon" aria-hidden="true"><svg 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fill="#EFA75B"/><path d="M31.963 50.968c-.197-.004-.358-.157-.372-.353-.018-.207.158-.378.364-.354 3.245-.26 3.505-2.156 3.608-2.25-.006-.19.183-.325.362-.26.193.01.35.16.363.354 0 .084 0 1.906 3.422 2 .192.008.348.16.362.353-.018.19-.172.34-.363.353-1.352.11-2.68-.4-3.61-1.386-.095-.096-.16-.22-.185-.353-.982 1.174-2.423 1.866-3.952 1.898z" fill="#151841"/><path d="M32.14 43.427c.186-.52 3.608.083 3.608.083s2.975-.688 3.422.084c-.05.288-.175.557-.363.78-.515-.056-1.037.004-1.525.178-.333.61-.488 1.304-.446 2-.222.394-.574.7-.995.864-.398-.112-.75-.354-.994-.688.047-.75-.146-1.496-.55-2.13-.27-.26-1.264.084-1.626-.083l-.53-1.088zm6.89.242c-.05.286-.175.556-.363.78-.503-.063-1.015-.012-1.497.148-.333.612-.487 1.305-.446 2-.222.394-.574.7-.995.864-.4-.112-.75-.354-.996-.688.053-.76-.14-1.515-.55-2.157-.268-.26-1.263.084-1.626-.084-.26-.23-.45-.53-.55-.864" fill="#CF4A27"/><path d="M35.748 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2.334.725-.13.837-1.46.93-2.13h.112c.937.492 1.647 1.33 1.98 2.334-.388.176-.793.31-1.21.4zm18.365-2.864c-1.104-.145-2.215-.232-3.33-.26-.546-.01-1.093.05-1.626.176-1.166.483-2.08 1.425-2.53 2.604l-.158.79 1.795.623c.558.153 1.132.24 1.71.26h.28c3.245-.177 4.137-3.72 4.137-3.72l.084-.353zm-1.264 1.86c-.54 1.394-2.882 1.646-2.966 1.646-.517-.02-1.03-.11-1.525-.26-.186-.085-.633-.26-1.08-.43.374-.966 1.117-1.746 2.065-2.165 0 .68.158 1.953.81 2.083.65.13.613-1.535.566-2.26.934.005 1.865.064 2.79.177-.11.316-.473.65-.66 1.17z" fill="#151841"/><path d="M19.26 39.27c.535 1.362 1.56 2.473 2.874 3.115.534.312 1.204-.07 1.207-.69.002-.285-.15-.55-.397-.695-.918-.46-1.65-1.222-2.073-2.158-.344-.957-1.972-.52-1.61.428zm29.45 3.125c1.083-.59 2.01-1.428 2.706-2.446.3-.556-.112-1.228-.743-1.21-.293.007-.56.17-.698.428-.568.776-1.306 1.412-2.158 1.86-.394.23-.517.742-.27 1.125.263.376.773.482 1.163.242z" fill="#EFA75B" stroke-width="13"/><path d="M16.025 32.436c1.525-1.386 2.427-4.408 2.79-6.835-.084.354 2.613.43 4.138-1.208 1.078-1.125.446-2-.186-3.375-1.71-3.552-4.585-6.323-7.384-8.918-.716-.69-1.44-2.428-2.706-2-.995.353-.93 3.2-.716 4.073 1.09 7.448 4.065 18.263 4.065 18.263zm37.372-.78c-1.704-1.826-2.822-4.12-3.208-6.585 0 .354-2.614.354-4.056-1.29-.995-1.127-.362-1.86.363-3.117 1.86-3.198 4.863-5.718 7.746-8.136.81-.604 1.627-1.47 2.79-.93.994.428.715 2.334.548 3.115-1.083 5.72-2.48 11.376-4.183 16.943z" fill="#FFF"/><path d="M53.564 20.422c-1.98.51-4.138 1.636-5.105 3.487-.43-2.196 1.645-4.65 3.393-5.832.333-.21.312-.703-.037-.886-.162-.085-.357-.076-.512.022-2.157 1.562-4.417 4.5-3.784 7.188.076.262.354.41.614.325l-.075.28c-.085.603.93.864.994.26.446-2.158 2.706-3.376 4.77-3.897.372-.076.522-.526.27-.81-.133-.15-.342-.204-.53-.138zM17.457 18.06c-.55-.354-.995.428-.55.865 1.433 1.004 3.182 3.05 3.395 4.956-.93-1.86-3.05-2.975-5.105-3.486-.386-.005-.633.41-.445.747.042.076.103.14.176.184 2.073.52 4.324 1.73 4.77 3.896.106.328.5.46.78.26.273.192.653.06.745-.26.735-2.66-1.6-5.728-3.766-7.16z" fill="#F1662A"/></svg></span><p class="course-loading-overlay__message"><b class="course-loading-overlay__message-title">Loading…</b><br><span class="course-loading-overlay__message-text">Everything will be ready in few seconds</span></p></div></div><div class="course-layout__sidebar course-theory"><div class="course-theory__inner course-theory__inner--left-stub"><button class="course-theory__close icon-close icon-close--light" type="button">Close</button><ul class="course-tabs course-tabs--non-interactive course-layout__theory-heading js--theory-tabs"><li class="course-tabs__item course-tabs__item--external course-tab course-tab--centered"><span class="course-tab__icon"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-theory"></use></svg></span><span class="course-tab__title">Theory</span></li><li class="course-tabs__item course-tabs__item--internal course-tab course-tab--centered course-tab--active js--theory-tab__theory"><span class="course-tab__icon"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-theory"></use></svg></span><span class="course-tab__title">Theory</span></li><li class="course-tabs__item course-tabs__item--internal course-tab course-tab--centered js--theory-tab__comments"><span class="course-tab__icon"><svg aria-hidden="true" style="width: 16px; height: 16px; fill: #2e2c9c;"><use xlink:href="/img/sprites/up.svg#comment"></use></svg></span><span class="course-tab__title">Comments</span></li></ul><section class="course-theory__content"><div class="js--theory-pane__theory course-theory__content-inner"><h1 class="course-theory__content-heading">The “change” event</h1><div class="course-theory__content-text"><p>We found all of the elements in the list. Each element is a separate task. It consists of text and a field with the <code>checkbox</code> type. This element works like a switch or a flag: if the field is empty, the task has not yet been completed and is waiting for its turn. If there is a checkmark inside, then the task has been completed and it can be removed.</p><p>In order to do something with the tasks themselves, you need to catch situations where the user clicks on the checkbox and this element is selected. This is where events come in handy.</p><p>We could add a click event for the entire task or for the entire <code><li></code> element. However, this solution is not optimal. The user may accidentally click on a task without wanting to close it.</p><p>You can configure checkbox clicks to be caught. This option works quite well. However, there is another event that will also come in handy: <code>change</code>. It is triggered when the field state changes. In the case of checkboxes, it is triggered when the state changes from an unselected field to a selected one, and vice versa.</p><p>So far we have not found checkboxes inside list elements. Therefore, first let’s find the checkbox inside each task, position the handler, and output some message in the console. We have many elements, so the algorithm will have to be repeated several times. Therefore, we will use a function. In this task, we will prepare this function to work, but in the next one we will call it and check whether our handler really works. We already added a function declaration to the code for you.</p><p>If you forgot how to add handlers, you can look at the example below. It shows the syntax for adding a handler:</p><pre><code>element.addEventListener('change', function () {
…
});
</code></pre><p>And if you want to remember what the code from the example means, you can review <a href="/courses/javascript-browser/events/add-handler">this assignment</a> and <a href="/courses/javascript-browser/events/arrange-events">this one</a> as well.</p><p class="info info--frame-heading info--frame-heading--boremode info--gray">You may be surprised that we sort through the elements that are found using <code>querySelectorAll</code> in a loop, like a regular array. We can do that. Because <code>querySelectorAll</code> returns <b>a collection of elements</b>. It looks like an array, but it is not actually one. Therefore, we call collections <i>pseudo-arrays</i>. We will later discuss the differences between collections and arrays. For now, it’s sufficient to know that collections can be sorted in a loop, just like arrays. We have already encountered collections in the “Introduction to JavaScript in the browser” chapter. For example, we dealt with them in <a href="/courses/javascript-browser/browser-intro/query-selector-all">this assignment</a> as well as in <a href="/courses/javascript-browser/browser-intro/dom-collection">this one</a>.
</p></div></div><div class="js--theory-pane__comments hidden course-theory__content-inner"><div class="course-theory__content-text"><h2 class="course-theory__content-heading">Comments</h2><div id="disqus_thread"></div><script>
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</script><noscript>Please enable JavaScript to view the <a href="https://disqus.com/?ref_noscript">comments powered by Disqus.</a></noscript></div></div></section><div class="course-theory__controls"><button class="button button--close" type="button">To the task</button></div></div></div><div class="course-layout__column course-layout__column--left"><ul class="js--course-tabs course-tabs course-layout__course-tabs"><li class="js--editor-tab course-tabs__item course-tab course-tabs__item--limited course-tabs__item--limited-large course-tab--active" data-editor="html"><span class="course-tab__title course-tab__title--indent"><span class="course-tab__title-part course-tab__title-part--active">index.html</span></span><button class="js--editor-split course-tab__button course-tab__button--split" type="button"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-split"></use></svg><span class="tooltip tooltip--light tooltip--to-top tooltip--with-wrap tooltip--short course-tab__tooltip"><span class="tooltip__wrap">Split mode</span></span></button></li><li class="js--editor-tab course-tabs__item course-tab course-tabs__item--limited course-tabs__item--limited-large" data-editor="css"><span class="course-tab__title course-tab__title--indent"><span class="course-tab__title-part course-tab__title-part--active">style.css</span></span><button class="js--editor-split course-tab__button course-tab__button--split" type="button"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-split"></use></svg><span class="tooltip tooltip--light tooltip--to-top tooltip--with-wrap tooltip--short course-tab__tooltip"><span class="tooltip__wrap">Split mode</span></span></button></li><li class="js--editor-tab course-tabs__item course-tab course-tabs__item--limited course-tabs__item--limited-large" data-editor="js"><span class="course-tab__title course-tab__title--indent"><span class="course-tab__title-part course-tab__title-part--active">script.js</span></span><button class="js--editor-split course-tab__button course-tab__button--split" type="button"><svg aria-hidden="true"><use xlink:href="/img/sprites/courses.svg#icon-split"></use></svg><span class="tooltip tooltip--light tooltip--to-top tooltip--with-wrap tooltip--short course-tab__tooltip"><span class="tooltip__wrap">Split mode</span></span></button></li></ul><div class="course-layout__editors"><div class="js--editor course-editor course-layout__editor" id="" data-tab="html" data-split=""><span class="course-editor__label"><span class="course-editor__label-item">HTML</span><button class="course-editor__label-item course-editor__label-item--interactive hidden js--editor__unsplit-button course-editor__label-item--simple" title="No split" type="button"><svg width="7" height="10" viewBox="0 0 7 10" xmlns="http://www.w3.org/2000/svg"><g stroke="currentColor" fill="none" fill-rule="evenodd"><path stroke-linecap="round" d="M.6 3.503L3.443.518l2.842 2.985"></path><path d="M3.5 1.5v7.16" stroke-linecap="square"></path></g></svg></button></span><div class="course-editor__item" id="html-editor"><!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>The To-Do List</title>
<link href="style.css" rel="stylesheet">
</head>
<body>
<h1 class="visually-hidden">The To-Do List</h1>
<ul class="todo-list">
<li class="todo-list-item">
<label>
<input class="todo-list-input" type="checkbox">
<span>Feed the cat</span>
</label>
</li>
<li class="todo-list-item">
<label>
<input class="todo-list-input" type="checkbox">
<span>Leave the country</span>
</label>
</li>
<li class="todo-list-item">
<label>
<input class="todo-list-input" type="checkbox">
<span>Go for a run</span>
</label>
</li>
</ul>
<p class="empty-tasks hidden">All of the tasks have been completed. There are no new tasks.</p>
<form class="add-form" action="https://echo.htmlacademy.ru/courses" method="post">
<input class="add-form-input" type="text" aria-label="Task description" placeholder="For example, buy an elephant" required>
<button class="add-form-button" type="submit">Add new task</button>
</form>
<template id="task-template">
<li class="todo-list-item">
<label>
<input type="checkbox" class="todo-list-input">
<span></span>
</label>
</li>
</template>
<script src="script.js"></script>
</body>
</html>
</div></div><div class="js--editor course-editor course-layout__editor course-editor--hidden" id="" data-tab="css" data-split=""><span class="course-editor__label"><span class="course-editor__label-item">CSS</span><button class="course-editor__label-item course-editor__label-item--interactive hidden js--editor__unsplit-button course-editor__label-item--simple" title="No split" type="button"><svg width="7" height="10" viewBox="0 0 7 10" xmlns="http://www.w3.org/2000/svg"><g stroke="currentColor" fill="none" fill-rule="evenodd"><path stroke-linecap="round" d="M.6 3.503L3.443.518l2.842 2.985"></path><path d="M3.5 1.5v7.16" stroke-linecap="square"></path></g></svg></button></span><div class="course-editor__item" id="css-editor">@font-face {
font-weight: 400;
font-family: "Muller";
font-style: normal;
font-display: swap;
src: url("fonts/Muller.woff") format("woff");
}
body {
margin: 40px 32px;
font-size: 18px;
line-height: normal;
font-family: "Muller", sans-serif;
}
.visually-hidden,
.todo-list-input {
position: absolute;
width: 1px;
height: 1px;
margin: -1px;
padding: 0;
overflow: hidden;
white-space: nowrap;
border: 0;
clip: rect(0 0 0 0);
clip-path: inset(100%);
}
.hidden {
display: none;
}
.todo-list {
margin: 0;
padding: 0;
list-style: none;
}
.todo-list-item {
margin-bottom: 12px;
}
.todo-list-item label {
display: block;
padding: 12px 18px;
background-color: #ffffff;
border-radius: 4px;
box-shadow: 0 2px 5px rgba(0, 0, 0, 0.15);
cursor: pointer;
user-select: none;
}
.todo-list-item span {
display: flex;
align-items: center;
}
.todo-list-input + span::before {
content: "";
display: inline-block;
width: 16px;
height: 16px;
margin-right: 16px;
background-color: #ffffff;
border: 2px solid #69b253;
border-radius: 4px;
}
.todo-list-input:checked + span::before {
background-color: #69b253;
background-image: url("check-white.svg");
background-repeat: no-repeat;
background-position: center;
}
.todo-list-input:not(:checked):hover + span::before,
.todo-list-input:not(:checked):focus + span::before {
background-color: rgba(105, 178, 83, 0.2);
}
.empty-tasks {
color: #69b253;
}
.empty-tasks::before {
content: "";
width: 14px;
height: 13px;
margin-right: 13px;
background-image: url("check-green.svg");
background-repeat: no-repeat;
background-position: center;
}
.add-form {
display: flex;
}
.add-form-input {
flex-grow: 1;
box-sizing: border-box;
height: 46px;
margin-right: 16px;
padding: 12px;
font: inherit;
border: 1px solid #a1b5c4;
border-radius: 4px;
}
.add-form-input:focus {
border: 1px solid #69b253;
outline: none;
}
.add-form-input:hover {
box-shadow: 0 0 6px rgba(105, 178, 83, 0.6);
}
.add-form-input::placeholder {
color: #a1b5c4;
}
.add-form-button {
flex-shrink: 0;
padding: 12px;
font: inherit;
color: #ffffff;
background-color: #69b253;
border: none;
border-radius: 4px;
user-select: none;
touch-action: manipulation;
}
.add-form-button:hover,
.add-form-button:focus {
background-color: #5aa045;
outline: none;
}
.add-form-button:active {
background-color: #42862e;
}
</div></div><div class="js--editor course-editor course-layout__editor course-editor--hidden" id="" data-tab="js" data-split=""><span class="course-editor__label"><span class="course-editor__label-item">JavaScript</span><button class="course-editor__label-item course-editor__label-item--interactive hidden js--editor__unsplit-button course-editor__label-item--simple" title="No split" type="button"><svg width="7" height="10" viewBox="0 0 7 10" xmlns="http://www.w3.org/2000/svg"><g stroke="currentColor" fill="none" fill-rule="evenodd"><path stroke-linecap="round" d="M.6 3.503L3.443.518l2.842 2.985"></path><path d="M3.5 1.5v7.16" stroke-linecap="square"></path></g></svg></button></span><div class="course-editor__item" id="js-editor">var list = document.querySelector('.todo-list');
var items = list.querySelectorAll('.todo-list-item');
var addCheckHandler = function (item) {
// Write your code here
};
for (var i = 0; i < items.length; i++) {
console.log(items[i]);
}
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