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Debugging the code
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  • 1. What are you planning to do?
  • 2. The “change” event
  • 3. How the “change” event works
  • 4. Deleting the element from the list
  • 5. How to check the collection length
  • 6. Debugging the code
  • 7. Static and live collections
  • 8. Displaying the message on the page
  • 9. The “submit” event
  • 10. Cancelling the form submission
  • 11. How to obtain text from the input field
  • 12. Templates and the <template> tag
  • 13. The contents of the <template> tag, document-fragment
  • 14. Cloning and inserting elements, part 1
  • 15. Cloning and inserting elements, part 2
  • 16. Cloning and inserting elements, part 3
  • 17. Cloning and inserting elements, part 4
  • 18. How to clone elements
  • 19. Adding a new element to a list
  • 20. Deleting a new task in the list
  • 21. Clearing the input field
  • 22. Summary of “Actions with DOM”
  • 23. The third program: “Instant messenger”
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  • Theory
  • Theory
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Static and live collections

We discovered a problem: the length of the items collection does not change when tasks are deleted from the list. Why does this happen?

querySelectorAll finds all of the desired elements once, records them, and does nothing more. This code is static, and the changes in DOM do not affect it whatsoever. We can say that querySelectorAll works like any other variable that we have written some value to. Until we redefine the variable, it will contain the value that we wrote to it, regardless of what happens in the code.

Therefore, this collection is called static.

However, in addition to static collections, we also have live collections of elements. They are also called dynamic. Dynamic collections react to changes in DOM. If one of the elements in the collection is deleted from DOM, then it will also disappear from the collection. These are several ways of obtaining a live collection. One of them is through the use of children. This method is called in the parent element, and it gathers together all of the child elements into a dynamic collection. The syntax is as follows:

parentElement.children;

Let’s explore how live collections work in practice. Change querySelectorAll to children in our code, and see how the program now works.

NodeList is output in the console together with the collection. What is it?

It is a type of collection. This type returns querySelectorAll along with a number of other methods. One particular feature of this collection is that it can be used to store not only DOM elements, such as li or div, but also line breaks and the text content of elements in the form of separate collection elements. A NodeList can be static or dynamic. It depends on the method that is used to call it. You can read more about these types of collections in the specification and on MDN.

Comments

  • index.html
  • style.css
  • script.js
HTML
<!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>
CSS
@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; }
JavaScript
var list = document.querySelector('.todo-list'); var items = list.querySelectorAll('.todo-list-item'); var toggleEmptyListMessage = function () { console.log(items); if (items.length === 0) { console.log('All of the goals are completed!'); } }; var addCheckHandler = function (item) { var checkbox = item.querySelector('.todo-list-input'); checkbox.addEventListener('change', function () { item.remove(); toggleEmptyListMessage(); }); }; for (var i = 0; i < items.length; i++) { addCheckHandler(items[i]); }

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Goalscompleted
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    1. Change querySelectorAll('.todo-list-item') to children in the value of the items variable.
    2. Complete all of the goals and look at the console output. Get ready to see some magic.

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