1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889---
title: "Event Delegation: Handle Events Efficiently in JavaScript"
sidebarTitle: "Event Delegation"
description: "Learn event delegation in JavaScript. Handle events efficiently using bubbling, manage dynamic elements, reduce memory usage, and implement common patterns."
---
How do you handle click events on a list that could have 10, 100, or 1,000 items? What about elements that don't even exist yet — dynamically added after the page loads? If you're adding individual event listeners to each element, you're working too hard and using too much memory.
```javascript
// The problem: Adding listeners to every item doesn't scale
// ❌ This approach has issues
document.querySelectorAll('.todo-item').forEach(item => {
item.addEventListener('click', handleClick)
})
// What about items added later? They won't have listeners!
// The solution: Event delegation
// ✅ One listener handles all items, including future ones
document.querySelector('.todo-list').addEventListener('click', (event) => {
if (event.target.matches('.todo-item')) {
handleClick(event)
}
})
```
**Event delegation** is a technique that leverages [event bubbling](/beyond/concepts/event-bubbling-capturing) to handle events at a higher level in the DOM than the element where the event originated. Instead of attaching listeners to multiple child elements, you attach a single listener to a parent element and use `event.target` to determine which child triggered the event.
<Info>
**What you'll learn in this guide:**
- What event delegation is and how it works
- The difference between `event.target` and `event.currentTarget`
- How to use `matches()` and `closest()` for element filtering
- Handling events on dynamically added elements
- Performance benefits of delegation
- Common delegation patterns for lists, tables, and menus
- When NOT to use event delegation
</Info>
<Warning>
**Prerequisite:** This guide assumes you understand [event bubbling and capturing](/beyond/concepts/event-bubbling-capturing). Event delegation relies on bubbling — the mechanism where events "bubble up" from child elements to their ancestors.
</Warning>
---
## What is Event Delegation?
**Event delegation** is a pattern where you attach a single event listener to a parent element to handle events on its child elements. When an event occurs on a child, it bubbles up to the parent, where the listener catches it and determines which specific child triggered the event. This approach reduces memory usage, simplifies code, and automatically handles dynamically added elements.
Think of event delegation like a receptionist at an office building. Instead of giving every employee their own personal doorbell, visitors ring one doorbell at the reception desk. The receptionist then determines who the visitor wants to see and routes them appropriately. One point of contact handles all visitors efficiently.
```
┌─────────────────────────────────────────────────────────────────────────────┐
│ EVENT DELEGATION FLOW │
├─────────────────────────────────────────────────────────────────────────────┤
│ │
│ User clicks a <button> inside a <div>: │
│ │
│ ┌──────────────────────────────────────────────────────────────────────┐ │
│ │ <div class="container"> ← Event listener attached HERE │ │
│ │ │ │ │
│ │ ├── <button>Save</button> ← Click happens HERE │ │
│ │ │ ↑ │ │
│ │ ├── <button>Delete</button> │ Event bubbles UP │ │
│ │ │ │ │ │
│ │ └── <button>Edit</button> │ │ │
│ │ │ │ │
│ └──────────────────────────────────┴───────────────────────────────────┘ │
│ │
│ 1. User clicks "Save" button │
│ 2. Event bubbles up to container │
│ 3. Container's listener catches the event │
│ 4. event.target identifies which button was clicked │
│ 5. Handler takes appropriate action │
│ │
└─────────────────────────────────────────────────────────────────────────────┘
```
---
## The Key Players: target, currentTarget, matches, and closest
Before diving into delegation patterns, you need to understand four essential tools:
### event.target vs event.currentTarget
These two properties are often confused but serve different purposes:
```javascript
// HTML: <ul id="menu"><li><button>Click</button></li></ul>
document.getElementById('menu').addEventListener('click', (event) => {
console.log('target:', event.target.tagName) // BUTTON (what was clicked)
console.log('currentTarget:', event.currentTarget.tagName) // UL (where listener is)
})
```
| Property | Returns | Use Case |
|----------|---------|----------|
| `event.target` | The element that **triggered** the event | Finding what was actually clicked |
| `event.currentTarget` | The element that **has the listener** | Referencing the delegating parent |
```javascript
// Visual example: Click on the inner span
// <div id="outer">
// <p>
// <span>Click me</span>
// </p>
// </div>
document.getElementById('outer').addEventListener('click', (event) => {
// If user clicks the <span>:
console.log(event.target) // <span>Click me</span>
console.log(event.currentTarget) // <div id="outer">
// target changes based on what's clicked
// currentTarget is always the element with the listener
})
```
### Element.matches() — Checking Element Identity
The [`matches()`](https://developer.mozilla.org/en-US/docs/Web/API/Element/matches) method tests whether an element matches a CSS selector. It's essential for filtering which elements should trigger your handler:
```javascript
document.querySelector('.container').addEventListener('click', (event) => {
// Check if clicked element is a button
if (event.target.matches('button')) {
console.log('Button clicked!')
}
// Check for specific class
if (event.target.matches('.delete-btn')) {
console.log('Delete button clicked!')
}
// Check for data attribute
if (event.target.matches('[data-action]')) {
const action = event.target.dataset.action
console.log('Action:', action)
}
// Complex selectors work too
if (event.target.matches('button.primary:not(:disabled)')) {
console.log('Enabled primary button clicked!')
}
})
```
### Element.closest() — Finding Ancestor Elements
The [`closest()`](https://developer.mozilla.org/en-US/docs/Web/API/Element/closest) method traverses up the DOM tree to find the nearest ancestor (or the element itself) that matches a selector. This is crucial when the actual click target is a nested element:
```javascript
// Problem: User might click the icon inside the button
// <button class="action-btn">
// <svg class="icon">...</svg>
// <span>Delete</span>
// </button>
document.querySelector('.container').addEventListener('click', (event) => {
// event.target might be the <svg> or <span>, not the <button>!
// Solution: Use closest() to find the button ancestor
const button = event.target.closest('.action-btn')
if (button) {
console.log('Action button clicked!')
// button is the <button> element, regardless of what was clicked inside
}
})
```
```
┌─────────────────────────────────────────────────────────────────────────────┐
│ closest() TRAVERSAL EXAMPLE │
├─────────────────────────────────────────────────────────────────────────────┤
│ │
│ Click on <svg> inside button: │
│ │
│ event.target = <svg> │
│ │ │
│ ▼ │
│ event.target.closest('.action-btn') │
│ │ │
│ ┌────────────┴────────────┐ │
│ │ Check: Does <svg> │ │
│ │ match '.action-btn'? │ NO │
│ └────────────┬────────────┘ │
│ │ Move UP to parent │
│ ▼ │
│ ┌────────────────────────────┐ │
│ │ Check: Does <button> │ │
│ │ match '.action-btn'? │ YES ──► Returns <button> │
│ └────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────────────────────┘
```
---
## Basic Event Delegation Pattern
Here's the fundamental pattern for event delegation:
```javascript
// Step 1: Attach listener to parent container
document.querySelector('.parent-container').addEventListener('click', (event) => {
// Step 2: Identify the target element
const target = event.target
// Step 3: Check if target matches what we're looking for
if (target.matches('.child-element')) {
// Step 4: Handle the event
handleChildClick(target)
}
})
```
### Example: Clickable List Items
```javascript
// HTML:
// <ul id="todo-list">
// <li data-id="1">Buy groceries</li>
// <li data-id="2">Walk the dog</li>
// <li data-id="3">Finish report</li>
// </ul>
const todoList = document.getElementById('todo-list')
todoList.addEventListener('click', (event) => {
// Check if an <li> was clicked
const item = event.target.closest('li')
if (item) {
const id = item.dataset.id
console.log(`Clicked todo item with id: ${id}`)
item.classList.toggle('completed')
}
})
// This handles all existing items AND any items added later!
```
---
## Handling Dynamic Elements
One of the biggest advantages of event delegation is handling elements that are added to the DOM after the page loads:
```javascript
// Without delegation: New items don't work!
function addTodoWithoutDelegation(text) {
const li = document.createElement('li')
li.textContent = text
// You'd have to manually add a listener to each new element
li.addEventListener('click', handleClick) // Tedious and error-prone!
document.getElementById('todo-list').appendChild(li)
}
// With delegation: New items automatically work!
function addTodoWithDelegation(text) {
const li = document.createElement('li')
li.textContent = text
// No need to add individual listeners
// The parent's delegated listener handles it automatically
document.getElementById('todo-list').appendChild(li)
}
// The delegated listener on the parent handles all items
document.getElementById('todo-list').addEventListener('click', (event) => {
if (event.target.matches('li')) {
event.target.classList.toggle('completed')
}
})
```
### Real-World Example: Dynamic Table
```javascript
// Imagine a table that gets rows from an API
const tableBody = document.querySelector('#users-table tbody')
// One listener handles all row actions
tableBody.addEventListener('click', (event) => {
const button = event.target.closest('button')
if (!button) return
const row = button.closest('tr')
const userId = row.dataset.userId
if (button.matches('.edit-btn')) {
editUser(userId)
} else if (button.matches('.delete-btn')) {
deleteUser(userId)
row.remove()
} else if (button.matches('.view-btn')) {
viewUser(userId)
}
})
// Later, when new data arrives:
async function loadUsers() {
const users = await fetch('/api/users').then(r => r.json())
users.forEach(user => {
const row = document.createElement('tr')
row.dataset.userId = user.id
row.innerHTML = `
<td>${user.name}</td>
<td>${user.email}</td>
<td>
<button class="view-btn">View</button>
<button class="edit-btn">Edit</button>
<button class="delete-btn">Delete</button>
</td>
`
tableBody.appendChild(row)
})
// All buttons automatically work without adding individual listeners!
}
```
---
## Common Delegation Patterns
### Pattern 1: Action Buttons with data-action
Use `data-action` attributes to specify what each element should do:
```javascript
// HTML:
// <div id="toolbar">
// <button data-action="save">Save</button>
// <button data-action="load">Load</button>
// <button data-action="delete">Delete</button>
// </div>
const actions = {
save() {
console.log('Saving...')
},
load() {
console.log('Loading...')
},
delete() {
console.log('Deleting...')
}
}
document.getElementById('toolbar').addEventListener('click', (event) => {
const action = event.target.dataset.action
if (action && actions[action]) {
actions[action]()
}
})
```
### Pattern 2: Tab Interface
```javascript
// HTML:
// <div class="tabs">
// <button class="tab" data-tab="home">Home</button>
// <button class="tab" data-tab="profile">Profile</button>
// <button class="tab" data-tab="settings">Settings</button>
// </div>
// <div class="tab-content" id="home">Home content</div>
// <div class="tab-content" id="profile">Profile content</div>
// <div class="tab-content" id="settings">Settings content</div>
document.querySelector('.tabs').addEventListener('click', (event) => {
const tab = event.target.closest('.tab')
if (!tab) return
// Remove active class from all tabs
document.querySelectorAll('.tab').forEach(t => t.classList.remove('active'))
tab.classList.add('active')
// Hide all content, show selected
const tabId = tab.dataset.tab
document.querySelectorAll('.tab-content').forEach(content => {
content.hidden = content.id !== tabId
})
})
```
### Pattern 3: Expandable/Collapsible Sections
```javascript
// HTML:
// <div class="accordion">
// <div class="accordion-item">
// <button class="accordion-header">Section 1</button>
// <div class="accordion-content">Content 1...</div>
// </div>
// <div class="accordion-item">
// <button class="accordion-header">Section 2</button>
// <div class="accordion-content">Content 2...</div>
// </div>
// </div>
document.querySelector('.accordion').addEventListener('click', (event) => {
const header = event.target.closest('.accordion-header')
if (!header) return
const item = header.closest('.accordion-item')
const content = item.querySelector('.accordion-content')
const isExpanded = item.classList.contains('expanded')
// Toggle this section
item.classList.toggle('expanded')
content.hidden = isExpanded
// Optional: Close other sections (for exclusive accordion)
// document.querySelectorAll('.accordion-item').forEach(otherItem => {
// if (otherItem !== item) {
// otherItem.classList.remove('expanded')
// otherItem.querySelector('.accordion-content').hidden = true
// }
// })
})
```
### Pattern 4: Form Validation
```javascript
// Delegate input validation to the form
document.querySelector('#signup-form').addEventListener('input', (event) => {
const input = event.target
if (input.matches('[data-validate]')) {
validateInput(input)
}
})
function validateInput(input) {
const type = input.dataset.validate
let isValid = true
let message = ''
switch (type) {
case 'email':
isValid = /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(input.value)
message = isValid ? '' : 'Please enter a valid email'
break
case 'required':
isValid = input.value.trim().length > 0
message = isValid ? '' : 'This field is required'
break
case 'minlength':
const min = parseInt(input.dataset.minlength, 10)
isValid = input.value.length >= min
message = isValid ? '' : `Minimum ${min} characters required`
break
}
input.classList.toggle('invalid', !isValid)
input.nextElementSibling.textContent = message
}
```
---
## Performance Benefits
Event delegation significantly reduces memory usage when dealing with many elements:
```javascript
// Without delegation: 1000 listeners
const items = document.querySelectorAll('.item') // 1000 items
items.forEach(item => {
item.addEventListener('click', handleClick) // 1000 listeners created!
})
// With delegation: 1 listener
document.querySelector('.container').addEventListener('click', (event) => {
if (event.target.matches('.item')) {
handleClick(event)
}
})
// Only 1 listener, handles all 1000+ items!
```
| Approach | Listeners | Memory Impact | Dynamic Elements |
|----------|-----------|---------------|------------------|
| Individual listeners on 1,000 items | 1,000 | High | Must add manually |
| Event delegation | 1 | Low | Automatic |
---
## Limitations and Edge Cases
### Events That Don't Bubble
Some events don't bubble and can't be delegated in the traditional way:
```javascript
// These events DON'T bubble:
// - focus / blur
// - mouseenter / mouseleave
// - load / unload / scroll (on elements)
// Solution 1: Use capturing phase
document.addEventListener('focus', (event) => {
if (event.target.matches('input')) {
console.log('Input focused')
}
}, true) // true = capture phase
// Solution 2: Use bubbling alternatives
// Instead of focus/blur, use focusin/focusout (they bubble!)
document.querySelector('.form').addEventListener('focusin', (event) => {
if (event.target.matches('input')) {
event.target.classList.add('focused')
}
})
document.querySelector('.form').addEventListener('focusout', (event) => {
if (event.target.matches('input')) {
event.target.classList.remove('focused')
}
})
```
### stopPropagation Interference
If child elements stop propagation, delegation won't work:
```javascript
// This child listener prevents delegation
childElement.addEventListener('click', (event) => {
event.stopPropagation() // Parent never receives the event!
// Do something...
})
// Avoid using stopPropagation unless absolutely necessary
// Consider using event.stopImmediatePropagation() only for specific cases
```
### Verifying the Element is Within Your Container
With nested tables or complex structures, ensure the target is actually within your container:
```javascript
// Problem with nested structures
document.querySelector('#outer-table').addEventListener('click', (event) => {
const td = event.target.closest('td')
// td might be from a nested table, not our table!
if (td && event.currentTarget.contains(td)) {
// Now we're sure td belongs to our table
handleCellClick(td)
}
})
```
---
## When NOT to Use Event Delegation
Event delegation isn't always the best choice:
```javascript
// ❌ DON'T delegate when:
// 1. You have only one element
const singleButton = document.querySelector('#submit-btn')
singleButton.addEventListener('click', handleSubmit) // Direct is fine
// 2. You need to prevent default behavior immediately
// (delegation adds slight delay due to bubbling)
// 3. The event doesn't bubble (without capture workaround)
// 4. Performance-critical scenarios where event.target checks add overhead
// (extremely rare in practice)
// ✅ DO use delegation when:
// - Handling many similar elements
// - Elements are added/removed dynamically
// - You want cleaner, more maintainable code
// - Memory efficiency is important
```
---
## Common Mistakes
### Mistake 1: Forgetting closest() for Nested Elements
```javascript
// ❌ WRONG: Only works if you click exactly on the button, not its children
container.addEventListener('click', (event) => {
if (event.target.matches('.btn')) {
// Fails if user clicks on <span> inside button!
}
})
// ✅ CORRECT: Works regardless of where inside the button you click
container.addEventListener('click', (event) => {
const btn = event.target.closest('.btn')
if (btn) {
// Works for button and all its children
}
})
```
### Mistake 2: Not Checking Container Boundaries
```javascript
// ❌ WRONG: Might catch elements from nested structures
table.addEventListener('click', (event) => {
const row = event.target.closest('tr')
if (row) {
// Could be a row from a nested table!
}
})
// ✅ CORRECT: Verify the element is within our container
table.addEventListener('click', (event) => {
const row = event.target.closest('tr')
if (row && table.contains(row)) {
// Definitely our row
}
})
```
### Mistake 3: Over-delegating
```javascript
// ❌ WRONG: Delegating at document level for everything
document.addEventListener('click', (event) => {
// This catches EVERY click on the page!
if (event.target.matches('.my-button')) {
// ...
}
})
// ✅ CORRECT: Delegate at the appropriate container level
document.querySelector('.my-component').addEventListener('click', (event) => {
if (event.target.matches('.my-button')) {
// Scoped to just this component
}
})
```
---
## Key Takeaways
<Info>
**The key things to remember:**
1. **Event delegation uses bubbling** — Attach one listener to a parent instead of many listeners to children. Events bubble up from the clicked element to the parent.
2. **event.target vs event.currentTarget** — `target` is what was clicked; `currentTarget` is where the listener is attached. Use `target` to identify which child triggered the event.
3. **matches() filters elements** — Use `event.target.matches(selector)` to check if the clicked element matches your criteria.
4. **closest() handles nested elements** — When buttons contain icons or spans, use `event.target.closest(selector)` to find the actual clickable element.
5. **Dynamic elements work automatically** — Elements added after page load are handled without adding new listeners.
6. **Memory efficient** — One listener instead of hundreds or thousands reduces memory usage significantly.
7. **Not all events bubble** — `focus`, `blur`, `mouseenter`, and `mouseleave` don't bubble. Use `focusin`/`focusout` or capture phase instead.
8. **Scope appropriately** — Delegate at the nearest common ancestor, not always at `document` level.
9. **Verify container boundaries** — With nested structures, use `container.contains(element)` to ensure the target is within your container.
10. **Keep handlers organized** — Use `data-action` attributes and action objects to keep delegation logic clean and maintainable.
</Info>
---
## Test Your Knowledge
<AccordionGroup>
<Accordion title="Question 1: What is the main benefit of event delegation?">
**Answer:**
Event delegation provides several key benefits:
1. **Memory efficiency** — One listener handles many elements instead of attaching individual listeners to each
2. **Dynamic element handling** — Elements added after page load automatically work without adding new listeners
3. **Cleaner code** — Centralized event handling logic instead of scattered listeners
4. **Easier maintenance** — Changes only need to be made in one place
```javascript
// One listener handles all current and future list items
list.addEventListener('click', (event) => {
if (event.target.matches('li')) {
handleItemClick(event.target)
}
})
```
</Accordion>
<Accordion title="Question 2: When should you use closest() instead of matches()?">
**Answer:**
Use `closest()` when the actual click target might be a nested element inside the element you care about:
```javascript
// Button structure: <button class="btn"><svg>...</svg><span>Click</span></button>
// ❌ matches() fails if user clicks the <svg> or <span>
if (event.target.matches('.btn')) { } // false when clicking icon!
// ✅ closest() finds the button even when clicking nested elements
const btn = event.target.closest('.btn') // finds parent button
if (btn) { } // works!
```
Use `closest()` when:
- Elements contain icons, images, or nested markup
- You need to find a specific ancestor element
- You want to handle clicks anywhere within a complex element
</Accordion>
<Accordion title="Question 3: Why do focus and blur events require special handling?">
**Answer:**
The `focus` and `blur` events **don't bubble** by default, so they can't be caught by a parent using standard delegation:
```javascript
// ❌ This won't work - focus doesn't bubble
form.addEventListener('focus', handler)
// ✅ Solution 1: Use capture phase
form.addEventListener('focus', handler, true)
// ✅ Solution 2: Use focusin/focusout (they bubble!)
form.addEventListener('focusin', handler) // bubbling equivalent of focus
form.addEventListener('focusout', handler) // bubbling equivalent of blur
```
Other non-bubbling events include: `mouseenter`, `mouseleave`, `load`, `unload`, and `scroll` (on elements).
</Accordion>
<Accordion title="Question 4: How do you handle multiple action types with delegation?">
**Answer:**
Use `data-action` attributes to specify actions, and map them to handler functions:
```javascript
// HTML
// <button data-action="save">Save</button>
// <button data-action="delete">Delete</button>
// JavaScript
const actions = {
save() { console.log('Saving...') },
delete() { console.log('Deleting...') }
}
container.addEventListener('click', (event) => {
const action = event.target.dataset.action
if (action && actions[action]) {
actions[action]()
}
})
```
This pattern is clean, extensible, and keeps your delegation logic organized.
</Accordion>
<Accordion title="Question 5: What's the difference between event.target and event.currentTarget?">
**Answer:**
| Property | Returns | When to use |
|----------|---------|-------------|
| `event.target` | Element that **triggered** the event | Identifying which child was clicked |
| `event.currentTarget` | Element that **has the listener** | Referencing the delegating parent |
```javascript
// <ul id="list"><li><button>Click</button></li></ul>
document.getElementById('list').addEventListener('click', (event) => {
console.log(event.target) // <button> (what was clicked)
console.log(event.currentTarget) // <ul> (where listener is attached)
})
```
`target` changes based on what's clicked; `currentTarget` is always the element with the listener.
</Accordion>
<Accordion title="Question 6: How do you verify an element is within your container with nested structures?">
**Answer:**
Use `container.contains(element)` to verify the target element is actually within your container:
```javascript
// Problem: With nested tables, closest('tr') might find a row
// from an inner table, not your table
table.addEventListener('click', (event) => {
const row = event.target.closest('tr')
// ❌ Wrong: row might be from nested table
if (row) { handleRow(row) }
// ✅ Correct: verify row is within our table
if (row && table.contains(row)) { handleRow(row) }
})
```
This is especially important with complex layouts, nested components, or when working with third-party widgets that might be inserted into your container.
</Accordion>
</AccordionGroup>
---
## Related Concepts
<CardGroup cols={2}>
<Card title="Event Bubbling & Capturing" icon="arrow-up" href="/beyond/concepts/event-bubbling-capturing">
Understand the event propagation mechanism that makes delegation possible
</Card>
<Card title="Custom Events" icon="bolt" href="/beyond/concepts/custom-events">
Learn to create and dispatch your own events that work with delegation
</Card>
<Card title="DOM Manipulation" icon="code" href="/concepts/dom">
Master the Document Object Model and element selection methods
</Card>
<Card title="Callbacks" icon="phone" href="/concepts/callbacks">
Understand callback functions used as event handlers
</Card>
</CardGroup>
---
## Reference
<CardGroup cols={2}>
<Card title="Event.target — MDN" icon="book" href="https://developer.mozilla.org/en-US/docs/Web/API/Event/target">
Official documentation for the target property that identifies the event origin
</Card>
<Card title="Event.currentTarget — MDN" icon="book" href="https://developer.mozilla.org/en-US/docs/Web/API/Event/currentTarget">
Documentation for currentTarget, which identifies where the listener is attached
</Card>
<Card title="Element.closest() — MDN" icon="book" href="https://developer.mozilla.org/en-US/docs/Web/API/Element/closest">
Reference for the closest() method used to find ancestor elements
</Card>
<Card title="Element.matches() — MDN" icon="book" href="https://developer.mozilla.org/en-US/docs/Web/API/Element/matches">
Documentation for testing if an element matches a CSS selector
</Card>
</CardGroup>
## Articles
<CardGroup cols={2}>
<Card title="Event Delegation — JavaScript.info" icon="newspaper" href="https://javascript.info/event-delegation">
Comprehensive tutorial with interactive examples covering delegation patterns, the behavior pattern, and practical exercises
</Card>
<Card title="Event Bubbling — MDN Learn" icon="newspaper" href="https://developer.mozilla.org/en-US/docs/Learn_web_development/Core/Scripting/Event_bubbling">
MDN's guide to event bubbling with clear explanations of target vs currentTarget and delegation examples
</Card>
<Card title="How JavaScript Event Delegation Works — David Walsh" icon="newspaper" href="https://davidwalsh.name/event-delegate">
Classic article explaining event delegation fundamentals with practical code examples
</Card>
<Card title="DOM Events Guide — MDN" icon="newspaper" href="https://developer.mozilla.org/en-US/docs/Web/API/Document_Object_Model/Events">
Comprehensive MDN guide to working with events in the DOM, including propagation and delegation
</Card>
</CardGroup>
## Videos
<CardGroup cols={2}>
<Card title="Event Delegation — Web Dev Simplified" icon="video" href="https://www.youtube.com/watch?v=XF1_MlZ5l6M">
Clear explanation of event delegation with visual examples showing how bubbling enables this pattern
</Card>
<Card title="JavaScript Event Delegation — Traversy Media" icon="video" href="https://www.youtube.com/watch?v=3KJI1WZGDrg">
Practical walkthrough building a dynamic list with delegated event handling
</Card>
<Card title="Event Bubbling and Delegation — The Net Ninja" icon="video" href="https://www.youtube.com/watch?v=aVeQ4shbNls">
Part of a comprehensive JavaScript DOM series covering bubbling and delegation together
</Card>
</CardGroup>