1.2 A function object that will be invoked for each element in the current set. Pass each element in the current matched set through a function, producing a new jQuery object containing the return values.

As the return value is a jQuery-wrapped array, it's very common to get() the returned object to work with a basic array.

The .map() method is particularly useful for getting or setting the value of a collection of elements. Consider a form with a set of checkboxes in it:

<form method="post" action="">
  <fieldset>
    <div>
      <label for="two">2</label>
      <input type="checkbox" value="2" id="two" name="number[]">
    </div>
    <div>
      <label for="four">4</label>
      <input type="checkbox" value="4" id="four" name="number[]">
    </div>
    <div>
      <label for="six">6</label>
      <input type="checkbox" value="6" id="six" name="number[]">
    </div>
    <div>
      <label for="eight">8</label>
      <input type="checkbox" value="8" id="eight" name="number[]">
    </div>
  </fieldset>
</form>

We can get a comma-separated list of checkbox IDs:

$(':checkbox').map(function() {
  return this.id;
}).get().join(',');

The result of this call is the string, "two,four,six,eight".

Within the callback function, this refers to the current DOM element for each iteration. The function can return an individual data item or an array of data items to be inserted into the resulting set. If an array is returned, the elements inside the array are inserted into the set. If the function returns null or undefined, no element will be inserted.

Build a list of all the values within a form. Values:

]]> A contrived example to show some functionality.

").text($(this).text()).get(0);
  if (index == 0) {
    /* make the first item all caps */
    $(replacement).text($(replacement).text().toUpperCase());
  } else if (index == 1 || index == 3) {
    /* delete the second and fourth items */
    replacement = null;
  } else if (index == 2) {
    /* make two of the third item and add some text */
    replacement = [replacement,$("

").get(0)];
    $(replacement[0]).append(" - A");
    $(replacement[1]).append("Extra  - B");
  }

  /* replacement will be a dom element, null,
     or an array of dom elements */
  return replacement;
});
$("#results").append(mappedItems);

]]>

First

Second

Third

Fourth

Fifth

]]> Equalize the heights of the divs.

]]>