← Back to jQuery Course | Chapter 7: DOM Traversing | Lesson 6 of 10

Filtering Nodes

filter() keeps elements that match a condition.

In this page:

  1. filter()
  2. not()
  3. eq()
  4. first() and last()
  5. Filtering Practice
Syntax
javascript 
$(selector).first();
$(selector).last();
$(selector).eq(index);
$(selector).filter(selector);
$(selector).not(selector);

filter()

.filter() narrows an existing jQuery selection down to only the elements that satisfy a selector or test function you supply. Unlike find(), it never looks at descendants -- it only keeps or drops elements already in the current selection.

Example: filter()

javascript 
<!DOCTYPE html>
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <style>
    button { padding:6px 14px; margin:4px; background:#2c6aa0; color:white; border:none; border-radius:4px; cursor:pointer; }
    #resetBtn { background:white; color:#2c6aa0; border:1px solid #2c6aa0; }
    #output { margin-top:10px; padding:8px; border:1px solid #ccc; border-radius:4px; background:#f7f7f7; font-family:monospace; min-height:24px; }
    #demo :where(p, div, span, li, h1, h2, h3, h4, td, th, blockquote, label, section, article, aside) { border:1px solid #4a7fb5; background:#eaf2fb; padding:6px 10px; margin:4px 0; border-radius:4px; }
    #demo :where(ul, ol) { border:1px dashed #888; background:#fafafa; padding:8px 8px 8px 32px; margin:6px 0; }
    #demo :where(table) { border-collapse:collapse; }
    #demo :where(td, th) { border-radius:0; }
    #demo :where(input, select, textarea) { margin:4px 0; }
  </style>
</head>
<body>
  <button id="runBtn">Run</button>
  <button id="resetBtn">Reset</button>
  <section id="demo">
    <li>One</li><li class="done">Two</li><li class="done">Three</li>

  </section>
  <div id="output"></div>
  <script>
    var original = $("#demo").html();

    $("#runBtn").click(function() {
      $("#output").text($("li").filter(".done").length);
    });

    $("#resetBtn").click(function() {
      $("#demo").html(original);
      $("#output").empty();
    });
  </script>
</body>
</html>

not()

not() removes elements that match a selector from the current selection, effectively the opposite of filter(). It's useful when it's easier to describe which elements to exclude than which ones to keep.

Example: not()

javascript 
<!DOCTYPE html>
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <style>
    button { padding:6px 14px; margin:4px; background:#2c6aa0; color:white; border:none; border-radius:4px; cursor:pointer; }
    #resetBtn { background:white; color:#2c6aa0; border:1px solid #2c6aa0; }
    #output { margin-top:10px; padding:8px; border:1px solid #ccc; border-radius:4px; background:#f7f7f7; font-family:monospace; min-height:24px; }
    #demo :where(p, div, span, li, h1, h2, h3, h4, td, th, blockquote, label, section, article, aside) { border:1px solid #4a7fb5; background:#eaf2fb; padding:6px 10px; margin:4px 0; border-radius:4px; }
    #demo :where(ul, ol) { border:1px dashed #888; background:#fafafa; padding:8px 8px 8px 32px; margin:6px 0; }
    #demo :where(table) { border-collapse:collapse; }
    #demo :where(td, th) { border-radius:0; }
    #demo :where(input, select, textarea) { margin:4px 0; }
  </style>
</head>
<body>
  <button id="runBtn">Run</button>
  <button id="resetBtn">Reset</button>
  <section id="demo">
    <li>One</li><li class="done">Two</li>

  </section>
  <div id="output"></div>
  <script>
    var original = $("#demo").html();

    $("#runBtn").click(function() {
      $("#output").text($("li").not(".done").length);
    });

    $("#resetBtn").click(function() {
      $("#demo").html(original);
      $("#output").empty();
    });
  </script>
</body>
</html>

eq()

eq() selects the element at a specific zero-based index within the current selection, similar to indexing into an array. Passing a negative index counts from the end of the selection instead of the start.

Example: eq()

javascript 
<!DOCTYPE html>
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <style>
    button { padding:6px 14px; margin:4px; background:#2c6aa0; color:white; border:none; border-radius:4px; cursor:pointer; }
    #resetBtn { background:white; color:#2c6aa0; border:1px solid #2c6aa0; }
    #output { margin-top:10px; padding:8px; border:1px solid #ccc; border-radius:4px; background:#f7f7f7; font-family:monospace; min-height:24px; }
    #demo :where(p, div, span, li, h1, h2, h3, h4, td, th, blockquote, label, section, article, aside) { border:1px solid #4a7fb5; background:#eaf2fb; padding:6px 10px; margin:4px 0; border-radius:4px; }
    #demo :where(ul, ol) { border:1px dashed #888; background:#fafafa; padding:8px 8px 8px 32px; margin:6px 0; }
    #demo :where(table) { border-collapse:collapse; }
    #demo :where(td, th) { border-radius:0; }
    #demo :where(input, select, textarea) { margin:4px 0; }
  </style>
</head>
<body>
  <button id="runBtn">Run</button>
  <button id="resetBtn">Reset</button>
  <section id="demo">
    <li>One</li><li>Two</li><li>Three</li>

  </section>
  <div id="output"></div>
  <script>
    var original = $("#demo").html();

    $("#runBtn").click(function() {
      $("#output").text($("li").eq(1).text());
    });

    $("#resetBtn").click(function() {
      $("#demo").html(original);
      $("#output").empty();
    });
  </script>
</body>
</html>

first() and last()

first() and last() make the two most common filtering tasks -- grabbing just the first or last matched element -- quick to write without needing eq(0) or a length calculation. Both are shorthand for the equivalent eq() call.

Example: first() and last()

javascript 
<!DOCTYPE html>
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <style>
    button { padding:6px 14px; margin:4px; background:#2c6aa0; color:white; border:none; border-radius:4px; cursor:pointer; }
    #resetBtn { background:white; color:#2c6aa0; border:1px solid #2c6aa0; }
    #output { margin-top:10px; padding:8px; border:1px solid #ccc; border-radius:4px; background:#f7f7f7; font-family:monospace; min-height:24px; }
    #demo :where(p, div, span, li, h1, h2, h3, h4, td, th, blockquote, label, section, article, aside) { border:1px solid #4a7fb5; background:#eaf2fb; padding:6px 10px; margin:4px 0; border-radius:4px; }
    #demo :where(ul, ol) { border:1px dashed #888; background:#fafafa; padding:8px 8px 8px 32px; margin:6px 0; }
    #demo :where(table) { border-collapse:collapse; }
    #demo :where(td, th) { border-radius:0; }
    #demo :where(input, select, textarea) { margin:4px 0; }
  </style>
</head>
<body>
  <button id="runBtn">Run</button>
  <button id="resetBtn">Reset</button>
  <section id="demo">
    <li>One</li><li>Two</li><li>Three</li>

  </section>
  <div id="output"></div>
  <script>
    var original = $("#demo").html();

    $("#runBtn").click(function() {
      $("#output").text($("li").first().text() + " " + $("li").last().text());
    });

    $("#resetBtn").click(function() {
      $("#demo").html(original);
      $("#output").empty();
    });
  </script>
</body>
</html>

Filtering Practice

Filtering helps you work with only the elements you actually need out of a broader selection, such as narrowing all list items down to just the ones marked as completed. It keeps later code simpler by acting on an already-precise set.

Example: Filtering Practice

javascript 
<!DOCTYPE html>
<html>
<head>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <style>
    button { padding:6px 14px; margin:4px; background:#2c6aa0; color:white; border:none; border-radius:4px; cursor:pointer; }
    #resetBtn { background:white; color:#2c6aa0; border:1px solid #2c6aa0; }
    #output { margin-top:10px; padding:8px; border:1px solid #ccc; border-radius:4px; background:#f7f7f7; font-family:monospace; min-height:24px; }
    #demo :where(p, div, span, li, h1, h2, h3, h4, td, th, blockquote, label, section, article, aside) { border:1px solid #4a7fb5; background:#eaf2fb; padding:6px 10px; margin:4px 0; border-radius:4px; }
    #demo :where(ul, ol) { border:1px dashed #888; background:#fafafa; padding:8px 8px 8px 32px; margin:6px 0; }
    #demo :where(table) { border-collapse:collapse; }
    #demo :where(td, th) { border-radius:0; }
    #demo :where(input, select, textarea) { margin:4px 0; }
  </style>
</head>
<body>
  <button id="runBtn">Run</button>
  <button id="resetBtn">Reset</button>
  <section id="demo">
    <li class="done">Task 1</li><li>Task 2</li>

  </section>
  <div id="output"></div>
  <script>
    var original = $("#demo").html();

    $("#runBtn").click(function() {
      $("#output").text($("li").filter(".done").length + " completed");
    });

    $("#resetBtn").click(function() {
      $("#demo").html(original);
      $("#output").empty();
    });
  </script>
</body>
</html>
Related Topics

Storing Metadata on DOM Nodes · Traversing Siblings Backward · Conditional Checks with is() and has() · Traversing Siblings Forward

{# common_mistakes/chapter_summary/browser_support: on Hindi pages the view already swaps in the hi_ translation fields (or blanks these out if untranslated), so this renders correctly for both languages without a lang_code check here. #}
Common Mistakes
  1. Confusing .filter("li") with .find("li"); .filter() narrows the current set while .find() searches inside it for descendants.
  2. Forgetting that .eq() is zero-based, so $("li").eq(1) selects the second item, not the first.
  3. Using .not(".done") and expecting it to change the page, when it only returns a smaller jQuery selection and does not remove any elements from the DOM.
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