Why JavaScript devours HTML: code examples

Likbez: HTML, CSS and JavaScript

HTML: for structure and semantics

CSS: to change the look

JavaScript: to implement behavior

Imperative vs declarative programming

• . «» , . ( ) : , , . , , . - «». Vanilla JavaScript , jQuery. JavaScript .
  
  • « X, Y, Z».
  • : , .selected; , .selected.

• . , . , , «» (), , - . , . (, React), , , . , , , , . , :
  
  • « XYZ. , , .
  • Example: this element has a .selected class if the user selected it.
  
  

HTML is a declarative language

<section>
  <h1>Hello</h1>
  <p>My name is Mike.</p>
</section>

1. Create a section element .
2. Create a level 1 header element ( h1 ).
3. Set the title element text to “Hello”.
4. Place the title element in the section element.
5. Create a paragraph element ( p ).
6. Set the text of the paragraph element to "My name is Mike".
7. Place a paragraph element in a section element .
8. Place the section element in an HTML document.
9. Display the document on the screen.

JavaScript is an imperative language

• a list of flagged flags, each line of which changes its color when selected;
• text below, for example, “1 of 4 selected”, which should be updated when the flags are changed;
• Select All button, which should be disabled if all the checkboxes are already selected;
• Select None button, which should be disabled if the checkboxes are not selected.

const captionText = document.getElementById('caption-text');
const checkAllButton = document.getElementById('check-all-button');
const uncheckAllButton = document.getElementById('uncheck-all-button');
const checkboxes = document.querySelectorAll('input[type="checkbox"]');

function updateSummary() {
  let numChecked = 0;
  checkboxes.forEach(function(checkbox) {
    if (checkbox.checked) {
      numChecked++;
    }
  });
  captionText.innerHTML = `${numChecked} of ${checkboxes.length} checked`;
  if (numChecked === 0) {
    checkAllButton.disabled = false;
    uncheckAllButton.disabled = true;
  } else {
    uncheckAllButton.disabled = false;
  }
  if (numChecked === checkboxes.length) {
    checkAllButton.disabled = true;
  }
}

checkAllButton.addEventListener('click', function() {
  checkboxes.forEach(function(checkbox) {
    checkbox.checked = true;
    checkbox.closest('tr').className = 'checked';
  });
  updateSummary();
});

uncheckAllButton.addEventListener('click', function() {
  checkboxes.forEach(function(checkbox) {
    checkbox.checked = false;
    checkbox.closest('tr').className = '';
  });
  updateSummary();
});

checkboxes.forEach(function(checkbox) {
  checkbox.addEventListener('change', function(event) {
    checkbox.closest('tr').className = checkbox.checked ? 'checked' : '';
    updateSummary();
  });
});

Headache as it is

• There are four row elements (a row of a table, it is a list), each of which contains a flag. The third flag is checked.

• There is a text “1 of 4 selected”.

• There is a Select All button that is turned on.

• There is a Select None button, which is disabled.

• Find the row containing the checkbox and add the CSS class .selected to it.

• Find all the flags in the list and calculate how many of them are marked and how many are not.

• Find the text and update it, indicating the correct number of selected purchases and their total number.

• Find the Select None button and turn it on if it was disabled.

• If all the checkboxes are now checked, find the Select All button and turn it off.

• Find the row containing the flag and remove the .selected class from it.

• Find all the checkboxes in the list and calculate how many of them are checked and how many are not.

• Find the resume text item and update it with the verified number and total.

• Find the Select All button and turn it on if it was disabled.

• If all the boxes are unchecked, find the Select None button and turn it off.

• Find all the checkboxes in the list and mark them.

• Find all the rows in the list and add the .selected class to them.

• Find the text and update it.

• Find the Select All button and turn it off.

• Find the Select None button and turn it on.

• Find all the checkboxes in the list and clear all the checkboxes.

• Find all the rows in the list and remove the .selected class from them.

• Find the resume text element and update it.

• Find the Select All button and turn it on.

• Find the Select None button and turn it off.

We are looking for the source of truth

Tell me what you want (what you really want)

• There is a list of true / false values ​​called checkboxValues ​​that shows which fields are marked.
  
  • Example: checkboxValues ​​\ u003d [false, false, true, false]
  • This list shows that we have four flags, only the third is set.

• For each value in checkboxValues ​​in the table, there is a row that:
  
  • has a CSS class called .selected if the value is true, and
  • contains a flag that is checked if the value is true.

• There is a text element that contains the text "{x} of {y} selected", where {x} is the number of true values ​​in checkboxValues, and {y} is the total number of values ​​in checkboxValues.
• There is a Select All button that is enabled if checkboxValues ​​has false values.
• Select None, , checkboxValues ​​ true.
• , checkboxValues.
• Select All , checkboxValues ​​ true.
• Select None checkboxValues ​​ false.

function ChecklistTable({ columns, rows, initialValues, ...otherProps }) {
  const [checkboxValues, setCheckboxValues] = React.useState(initialValues);
  
  function checkAllBoxes() {
    setCheckboxValues(new Array(rows.length).fill(true));
  }
  
  function uncheckAllBoxes() {
    setCheckboxValues(new Array(rows.length).fill(false));
  }
  
  function setCheckboxValue(rowIndex, checked) {
    const newValues = checkboxValues.slice();
    newValues[rowIndex] = checked;
    setCheckboxValues(newValues);
  }
  
  const numItems = checkboxValues.length;
  const numChecked = checkboxValues.filter(Boolean).length;
  
  return (
    <table className="pf-c-table pf-m-grid-lg" role="grid" {...otherProps}>
      <caption>
        <span>{numChecked} of {numItems} items checked</span>
        <button
          onClick={checkAllBoxes}
          disabled={numChecked === numItems}
          className="pf-c-button pf-m-primary"
          type="button"
        >
          Check all
        </button>
        <button
          onClick={uncheckAllBoxes}
          disabled={numChecked === 0}
          className="pf-c-button pf-m-secondary"
          type="button"
        >
          Uncheck all
        </button>
      </caption>
      <thead>
        <tr>
          <td />
          {columns.map(function(column) {
            return <th scope="col" key={column}>{column}</th>;
          })}
        </tr>
      </thead>
      <tbody>
        {rows.map(function(row, rowIndex) {
          const [firstCell, ...otherCells] = row;
          const labelId = `item-${rowIndex}-${firstCell}`;
          const isChecked = checkboxValues[rowIndex];
          return (
            <tr key={firstCell} className={isChecked ? 'checked' : ''}>
              <td className="pf-c-table__check">
                <input
                  type="checkbox"
                  name={firstCell}
                  aria-labelledby={labelId}
                  checked={isChecked}
                  onChange={function(event) {
                    setCheckboxValue(rowIndex, event.target.checked);
                  }}
                />
              </td>
              <th data-label={columns[0]}>
                <div id={labelId}>{firstCell}</div>
              </th>
              {otherCells.map(function(cell, cellIndex) {
                return (
                  <td key={cell} data-label={columns[1 + cellIndex]}>
                    {cell}
                  </td>
                );
              })}
            </tr>
          );
        })}
      </tbody>
    </table>
  );
};

function ShoppingList() {
  return (
    <ChecklistTable
      aria-label="Shopping list"
      columns={['Item', 'Quantity']}
      rows={[
        ['Sugar', '1 cup'],
        ['Butter', '½ cup'],
        ['Eggs', '2'],
        ['Milk', '½ cup'],
      ]}
      initialValues={[false, false, true, false]}
    />
  );
}

ReactDOM.render(
  <ShoppingList />,
  document.getElementById('shopping-list')
);

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