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666/**
* @vitest-environment jsdom
*/
import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
// ============================================================
// MUTATIONOBSERVER TESTS
// From mutation-observer.mdx
// ============================================================
describe('MutationObserver', () => {
let container
let observer
beforeEach(() => {
container = document.createElement('div')
container.id = 'test-container'
document.body.appendChild(container)
})
afterEach(() => {
if (observer) {
observer.disconnect()
observer = null
}
document.body.innerHTML = ''
vi.restoreAllMocks()
})
// ============================================================
// CREATING A MUTATIONOBSERVER
// From mutation-observer.mdx lines 75-120
// ============================================================
describe('Creating a MutationObserver', () => {
// From lines 75-85: Basic observer creation
it('should create observer with callback', () => {
const callback = vi.fn()
observer = new MutationObserver(callback)
expect(observer).toBeInstanceOf(MutationObserver)
})
// From lines 90-98: Observer receives mutations array
it('should call callback with mutations array when changes occur', async () => {
const mutations = []
observer = new MutationObserver((mutationList) => {
mutations.push(...mutationList)
})
observer.observe(container, { childList: true })
container.appendChild(document.createElement('span'))
// Wait for microtask
await Promise.resolve()
expect(mutations.length).toBe(1)
expect(mutations[0].type).toBe('childList')
})
// From lines 100-115: Processing mutation types
it('should report correct mutation type for childList changes', async () => {
let mutationType = null
observer = new MutationObserver((mutations) => {
mutationType = mutations[0].type
})
observer.observe(container, { childList: true })
container.appendChild(document.createElement('div'))
await Promise.resolve()
expect(mutationType).toBe('childList')
})
it('should report correct mutation type for attribute changes', async () => {
let mutationType = null
let attributeName = null
observer = new MutationObserver((mutations) => {
mutationType = mutations[0].type
attributeName = mutations[0].attributeName
})
observer.observe(container, { attributes: true })
container.setAttribute('data-test', 'value')
await Promise.resolve()
expect(mutationType).toBe('attributes')
expect(attributeName).toBe('data-test')
})
})
// ============================================================
// CONFIGURATION OPTIONS
// From mutation-observer.mdx lines 130-220
// ============================================================
describe('Configuration Options', () => {
// From lines 140-155: childList option
describe('childList option', () => {
it('should detect added nodes', async () => {
const addedNodes = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
addedNodes.push(...mutation.addedNodes)
}
})
observer.observe(container, { childList: true })
const newElement = document.createElement('span')
container.appendChild(newElement)
await Promise.resolve()
expect(addedNodes).toContain(newElement)
})
it('should detect removed nodes', async () => {
const child = document.createElement('span')
container.appendChild(child)
const removedNodes = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
removedNodes.push(...mutation.removedNodes)
}
})
observer.observe(container, { childList: true })
container.removeChild(child)
await Promise.resolve()
expect(removedNodes).toContain(child)
})
it('should detect innerHTML changes', async () => {
let mutationCount = 0
observer = new MutationObserver((mutations) => {
mutationCount = mutations.length
})
observer.observe(container, { childList: true })
container.innerHTML = '<p>New content</p>'
await Promise.resolve()
expect(mutationCount).toBeGreaterThan(0)
})
})
// From lines 160-180: attributes option
describe('attributes option', () => {
it('should detect setAttribute changes', async () => {
let changedAttribute = null
observer = new MutationObserver((mutations) => {
changedAttribute = mutations[0].attributeName
})
observer.observe(container, { attributes: true })
container.setAttribute('data-active', 'true')
await Promise.resolve()
expect(changedAttribute).toBe('data-active')
})
it('should detect classList changes', async () => {
let changedAttribute = null
observer = new MutationObserver((mutations) => {
changedAttribute = mutations[0].attributeName
})
observer.observe(container, { attributes: true })
container.classList.add('highlight')
await Promise.resolve()
expect(changedAttribute).toBe('class')
})
it('should detect id changes', async () => {
let changedAttribute = null
observer = new MutationObserver((mutations) => {
changedAttribute = mutations[0].attributeName
})
observer.observe(container, { attributes: true })
container.id = 'new-id'
await Promise.resolve()
expect(changedAttribute).toBe('id')
})
})
// From lines 185-200: attributeFilter option
describe('attributeFilter option', () => {
it('should only observe specified attributes', async () => {
const observedAttributes = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
observedAttributes.push(mutation.attributeName)
}
})
observer.observe(container, {
attributes: true,
attributeFilter: ['class', 'data-state']
})
container.classList.toggle('active')
container.dataset.state = 'loading'
container.setAttribute('title', 'Hello') // Should NOT be observed
await Promise.resolve()
expect(observedAttributes).toContain('class')
expect(observedAttributes).toContain('data-state')
expect(observedAttributes).not.toContain('title')
})
})
// From lines 205-220: attributeOldValue option
describe('attributeOldValue option', () => {
it('should include old value when attributeOldValue is true', async () => {
container.setAttribute('data-value', 'original')
let oldValue = null
let newValue = null
observer = new MutationObserver((mutations) => {
oldValue = mutations[0].oldValue
newValue = mutations[0].target.getAttribute(mutations[0].attributeName)
})
observer.observe(container, {
attributes: true,
attributeOldValue: true
})
container.setAttribute('data-value', 'updated')
await Promise.resolve()
expect(oldValue).toBe('original')
expect(newValue).toBe('updated')
})
})
})
// ============================================================
// SUBTREE OPTION
// From mutation-observer.mdx lines 280-320
// ============================================================
describe('Subtree Option', () => {
// From lines 285-300: Without subtree
it('should only observe direct children without subtree option', async () => {
const child = document.createElement('div')
const grandchild = document.createElement('span')
child.appendChild(grandchild)
container.appendChild(child)
const mutations = []
observer = new MutationObserver((mutationList) => {
mutations.push(...mutationList)
})
// Observe WITHOUT subtree
observer.observe(container, { childList: true })
// Add to grandchild - should NOT trigger
grandchild.appendChild(document.createElement('p'))
await Promise.resolve()
// No mutations expected since we're not watching subtree
expect(mutations.length).toBe(0)
})
// From lines 305-320: With subtree
it('should observe all descendants with subtree option', async () => {
const child = document.createElement('div')
const grandchild = document.createElement('span')
child.appendChild(grandchild)
container.appendChild(child)
const mutations = []
observer = new MutationObserver((mutationList) => {
mutations.push(...mutationList)
})
// Observe WITH subtree
observer.observe(container, { childList: true, subtree: true })
// Add to grandchild - SHOULD trigger
grandchild.appendChild(document.createElement('p'))
await Promise.resolve()
expect(mutations.length).toBe(1)
expect(mutations[0].target).toBe(grandchild)
})
})
// ============================================================
// MUTATIONRECORD PROPERTIES
// From mutation-observer.mdx lines 230-275
// ============================================================
describe('MutationRecord Properties', () => {
// From lines 240-260: addedNodes and removedNodes
it('should provide addedNodes in mutation record', async () => {
let record = null
observer = new MutationObserver((mutations) => {
record = mutations[0]
})
observer.observe(container, { childList: true })
const newElement = document.createElement('p')
container.appendChild(newElement)
await Promise.resolve()
expect(record.addedNodes.length).toBe(1)
expect(record.addedNodes[0]).toBe(newElement)
expect(record.removedNodes.length).toBe(0)
})
it('should provide removedNodes in mutation record', async () => {
const child = document.createElement('p')
container.appendChild(child)
let record = null
observer = new MutationObserver((mutations) => {
record = mutations[0]
})
observer.observe(container, { childList: true })
container.removeChild(child)
await Promise.resolve()
expect(record.removedNodes.length).toBe(1)
expect(record.removedNodes[0]).toBe(child)
expect(record.addedNodes.length).toBe(0)
})
// From lines 265-275: target property
it('should provide target element in mutation record', async () => {
let target = null
observer = new MutationObserver((mutations) => {
target = mutations[0].target
})
observer.observe(container, { attributes: true })
container.setAttribute('data-test', 'value')
await Promise.resolve()
expect(target).toBe(container)
})
})
// ============================================================
// DISCONNECTING AND CLEANUP
// From mutation-observer.mdx lines 330-380
// ============================================================
describe('Disconnecting and Cleanup', () => {
// From lines 335-345: disconnect() method
it('should stop observing after disconnect()', async () => {
let mutationCount = 0
observer = new MutationObserver(() => {
mutationCount++
})
observer.observe(container, { childList: true })
// First change - should be observed
container.appendChild(document.createElement('span'))
await Promise.resolve()
expect(mutationCount).toBe(1)
// Disconnect
observer.disconnect()
// Second change - should NOT be observed
container.appendChild(document.createElement('span'))
await Promise.resolve()
expect(mutationCount).toBe(1) // Still 1, not 2
})
// From lines 350-365: takeRecords() method
it('should return pending mutations with takeRecords()', async () => {
const callbackMutations = []
observer = new MutationObserver((mutations) => {
callbackMutations.push(...mutations)
})
observer.observe(container, { childList: true })
// Make changes
container.appendChild(document.createElement('span'))
container.appendChild(document.createElement('div'))
// Get pending mutations before they're delivered to callback
const pendingMutations = observer.takeRecords()
// These mutations are now "taken" and won't be delivered to callback
await Promise.resolve()
expect(pendingMutations.length).toBe(2)
expect(callbackMutations.length).toBe(0) // Callback never received them
})
})
// ============================================================
// FILTERING NODE TYPES
// From mutation-observer.mdx lines 440-470 (Common Mistakes)
// ============================================================
describe('Filtering Node Types', () => {
// From lines 445-465: Filter for elements only
it('should include text nodes in addedNodes', async () => {
const addedNodes = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
addedNodes.push(...mutation.addedNodes)
}
})
observer.observe(container, { childList: true })
// This adds a text node, not an element
container.textContent = 'Hello'
await Promise.resolve()
// Should have a text node
const hasTextNode = addedNodes.some(node => node.nodeType === Node.TEXT_NODE)
expect(hasTextNode).toBe(true)
})
it('should be able to filter for elements only', async () => {
const addedElements = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
for (const node of mutation.addedNodes) {
if (node.nodeType === Node.ELEMENT_NODE) {
addedElements.push(node)
}
}
}
})
observer.observe(container, { childList: true })
// Add text node (should be ignored)
container.appendChild(document.createTextNode('Hello'))
// Add element (should be captured)
const elem = document.createElement('span')
container.appendChild(elem)
await Promise.resolve()
expect(addedElements.length).toBe(1)
expect(addedElements[0]).toBe(elem)
})
})
// ============================================================
// CHARACTERDATA MUTATIONS
// From mutation-observer.mdx lines 110-115
// ============================================================
describe('characterData Mutations', () => {
it('should detect text content changes in text nodes', async () => {
const textNode = document.createTextNode('Initial text')
container.appendChild(textNode)
let mutationType = null
let oldValue = null
observer = new MutationObserver((mutations) => {
mutationType = mutations[0].type
oldValue = mutations[0].oldValue
})
observer.observe(container, {
characterData: true,
subtree: true,
characterDataOldValue: true
})
textNode.textContent = 'Updated text'
await Promise.resolve()
expect(mutationType).toBe('characterData')
expect(oldValue).toBe('Initial text')
})
})
// ============================================================
// REAL-WORLD USE CASES
// From mutation-observer.mdx lines 400-440
// ============================================================
describe('Real-World Use Cases', () => {
// From lines 405-420: Lazy loading images pattern
it('should detect images added to DOM for lazy loading', async () => {
const loadedImages = []
function loadImage(img) {
if (img.dataset.src) {
img.src = img.dataset.src
img.removeAttribute('data-src')
loadedImages.push(img)
}
}
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
for (const node of mutation.addedNodes) {
if (node.nodeType !== Node.ELEMENT_NODE) continue
if (node.matches && node.matches('img[data-src]')) {
loadImage(node)
}
if (node.querySelectorAll) {
node.querySelectorAll('img[data-src]').forEach(loadImage)
}
}
}
})
observer.observe(container, { childList: true, subtree: true })
// Add image with data-src
const img = document.createElement('img')
img.dataset.src = 'https://example.com/image.jpg'
container.appendChild(img)
await Promise.resolve()
expect(loadedImages.length).toBe(1)
expect(img.src).toBe('https://example.com/image.jpg')
expect(img.dataset.src).toBeUndefined()
})
// From lines 430-445: Removing unwanted elements
it('should detect and remove unwanted elements', async () => {
const removedElements = []
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
for (const node of mutation.addedNodes) {
if (node.nodeType !== Node.ELEMENT_NODE) continue
if (node.matches && node.matches('.ad-banner')) {
node.remove()
removedElements.push(node)
}
}
}
})
observer.observe(container, { childList: true, subtree: true })
// Simulate ad being injected
const ad = document.createElement('div')
ad.className = 'ad-banner'
container.appendChild(ad)
await Promise.resolve()
expect(removedElements.length).toBe(1)
expect(container.querySelector('.ad-banner')).toBeNull()
})
// From lines 450-465: Tracking class changes
it('should detect class changes on elements', async () => {
const element = document.createElement('div')
element.id = 'panel'
container.appendChild(element)
let isExpanded = false
observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
if (mutation.attributeName === 'class') {
isExpanded = mutation.target.classList.contains('expanded')
}
}
})
observer.observe(element, {
attributes: true,
attributeFilter: ['class']
})
element.classList.add('expanded')
await Promise.resolve()
expect(isExpanded).toBe(true)
})
})
// ============================================================
// MICROTASK TIMING
// From mutation-observer.mdx lines 385-400
// ============================================================
describe('Microtask Timing', () => {
it('should batch multiple changes into single callback', async () => {
let callbackCount = 0
let totalMutations = 0
observer = new MutationObserver((mutations) => {
callbackCount++
totalMutations += mutations.length
})
observer.observe(container, { childList: true })
// Make multiple changes synchronously
container.appendChild(document.createElement('div'))
container.appendChild(document.createElement('span'))
container.appendChild(document.createElement('p'))
await Promise.resolve()
// Should be batched into single callback
expect(callbackCount).toBe(1)
expect(totalMutations).toBe(3)
})
})
})