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  1. MDN Web Docs Glossary: Definitions of Web-related terms
  2. Nullish value
  1. MDN Web Docs Glossary
    1. Abstraction
    2. Accent
    3. Accessibility
    4. Accessibility tree
    5. Accessible name
    6. Adobe Flash
    7. Advance measure
    8. Ajax
    9. Algorithm
    10. Alignment container
    11. Alignment subject
    12. Alpha (alpha channel)
    13. ALPN
    14. API
    15. Apple Safari
    16. Application Context
    17. Argument
    18. ARIA
    19. ARPA
    20. ARPANET
    21. Array
    22. ASCII
    23. Asynchronous
    24. ATAG
    25. Attribute
    26. Bandwidth
    27. Base64
    28. Baseline
    29. Beacon
    30. Bézier curve
    31. BiDi
    32. BigInt
    33. Bitwise flags
    34. Blink
    35. Block
    36. Block cipher mode of operation
    37. Block-level content
    38. Boolean
    39. Bounding Box
    40. Breadcrumb
    41. Brotli
    42. Browser
    43. Browsing context
    44. Buffer
    45. Cache
    46. Cacheable
    47. CalDAV
    48. Call stack
    49. Callback function
    50. Canonical order
    51. Canvas
    52. Card sorting
    53. CardDAV
    54. Caret
    55. CDN
    56. Certificate authority
    57. Certified
    58. Challenge-response authentication
    59. Character
    60. Character encoding
    61. Character set
    62. Chrome
    63. CIA
    64. Cipher
    65. Cipher suite
    66. Ciphertext
    67. Class
    68. Clickjacking
    69. Closure
    70. CMS
    71. Code point
    72. Code splitting
    73. Code unit
    74. Codec
    75. Color wheel
    76. Compile
    77. Compile time
    78. Composite operation
    79. Computer Programming
    80. Conditional
    81. Constant
    82. Constructor
    83. Continuous Media
    84. Control flow
    85. Cookie
    86. Copyleft
    87. CORS
    88. CORS-safelisted request header
    89. CORS-safelisted response header
    90. Crawler
    91. CRLF
    92. Cross Axis
    93. Cross-site scripting (XSS)
    94. CRUD
    95. Cryptanalysis
    96. Cryptographic hash function
    97. Cryptography
    98. CSP
    99. CSRF
    100. CSS
    101. CSS Object Model (CSSOM)
    102. CSS pixel
    103. CSS preprocessor
    104. Data structure
    105. Database
    106. Decryption
    107. Deep copy
    108. Delta
    109. Denial of Service
    110. Descriptor (CSS)
    111. Deserialization
    112. Developer Tools
    113. Digest
    114. Digital certificate
    115. Distributed Denial of Service
    116. DMZ
    117. DNS
    118. Doctype
    119. Document directive
    120. Document environment
    121. DOM (Document Object Model)
    122. Domain
    123. Domain name
    124. Domain sharding
    125. Dominator
    126. DoS attack
    127. DSL
    128. DTLS (Datagram Transport Layer Security)
    129. DTMF (Dual-Tone Multi-Frequency signaling)
    130. Dynamic typing
    131. ECMA
    132. ECMAScript
    133. Effective connection type
    134. Element
    135. Encapsulation
    136. Encryption
    137. Endianness
    138. Engine
    139. Entity
    140. Entity header
    141. Enumerated
    142. eTLD
    143. Event
    144. Exception
    145. EXIF
    146. Expando
    147. Fallback alignment
    148. Falsy
    149. Favicon
    150. Fetch directive
    151. Fetch metadata request header
    152. Fingerprinting
    153. Firefox OS
    154. Firewall
    155. First contentful paint
    156. First CPU idle
    157. First input delay
    158. First interactive
    159. First Meaningful Paint
    160. First paint
    161. First-class Function
    162. Flex
    163. Flex Container
    164. Flex Item
    165. Flexbox
    166. Forbidden header name
    167. Forbidden response header name
    168. Fork
    169. Fragmentainer
    170. Frame rate (FPS)
    171. FTP
    172. FTU
    173. Function
    174. Fuzz testing
    175. Gamut
    176. Garbage collection
    177. Gecko
    178. General header
    179. GIF
    180. Git
    181. Global object
    182. Global scope
    183. Global variable
    184. Glyph
    185. Google Chrome
    186. GPL
    187. GPU
    188. Graceful degradation
    189. Grid
    190. Grid Areas
    191. Grid Axis
    192. Grid Cell
    193. Grid Column
    194. Grid container
    195. Grid Lines
    196. Grid Row
    197. Grid Tracks
    198. Guard
    199. Gutters
    200. GZip compression
    201. Hash
    202. Head
    203. High-level programming language
    204. HMAC
    205. Hoisting
    206. Host
    207. Hotlink
    208. Houdini
    209. HPKP
    210. HSTS
    211. HTML
    212. HTML5
    213. HTTP
    214. HTTP header
    215. HTTP/2
    216. HTTP/3
    217. HTTPS
    218. HTTPS RR
    219. Hyperlink
    220. Hypertext
    221. I18N
    222. IANA
    223. ICANN
    224. ICE
    225. IDE
    226. Idempotent
    227. Identifier
    228. IDL
    229. IETF
    230. IIFE
    231. IMAP
    232. Immutable
    233. IndexedDB
    234. Information architecture
    235. Inheritance
    236. Ink overflow
    237. Inline-level content
    238. Input method editor
    239. Instance
    240. Internationalization
    241. Internet
    242. Interpolation
    243. Intrinsic size
    244. IP Address
    245. IPv4
    246. IPv6
    247. IRC
    248. ISO
    249. ISP
    250. ITU
    251. Jank
    252. Java
    253. JavaScript
    254. JPEG
    255. JSON
    256. Key
    257. Keyword
    258. Largest contentful paint
    259. Latency
    260. Layout viewport
    261. Lazy load
    262. LGPL
    263. Ligature
    264. Literal
    265. Local scope
    266. Local variable
    267. Locale
    268. Localization
    269. Long task
    270. Loop
    271. Lossless compression
    272. Lossy compression
    273. LTR (Left To Right)
    274. Main Axis
    275. Main thread
    276. Markup
    277. MathML
    278. Media
    279. Metadata
    280. Method
    281. Microsoft Edge
    282. Microsoft Internet Explorer
    283. Middleware
    284. MIME
    285. MIME type
    286. Minification
    287. MitM
    288. Mixin
    289. Mobile First
    290. Modem
    291. Modularity
    292. Mozilla Firefox
    293. Mutable
    294. MVC
    295. Namespace
    296. NaN
    297. NAT
    298. Native
    299. Navigation directive
    300. Netscape Navigator
    301. Network throttling
    302. NNTP
    303. Node
    304. Node.js
    305. Non-normative
    306. Normative
    307. Null
    308. Nullish value
    309. Number
    310. Object
    311. Object reference
    312. OOP
    313. OpenGL
    314. OpenSSL
    315. Opera Browser
    316. Operand
    317. Operator
    318. Origin
    319. OTA
    320. OWASP
    321. P2P
    322. PAC
    323. Packet
    324. Page load time
    325. Page prediction
    326. Parameter
    327. Parent object
    328. Parse
    329. Parser
    330. Payload body
    331. Payload header
    332. PDF
    333. Perceived performance
    334. Percent-encoding
    335. PHP
    336. Pixel
    337. Placeholder names
    338. Plaintext
    339. Plugin
    340. PNG
    341. Polyfill
    342. Polymorphism
    343. POP3
    344. Port
    345. Prefetch
    346. Preflight request
    347. Prerender
    348. Presto
    349. Primitive
    350. Privileged
    351. Privileged code
    352. Progressive Enhancement
    353. Progressive web apps
    354. Promise
    355. Property
    356. Protocol
    357. Prototype
    358. Prototype-based programming
    359. Proxy server
    360. Pseudo-class
    361. Pseudo-element
    362. Pseudocode
    363. Public-key cryptography
    364. Python
    365. Quality values
    366. Quaternion
    367. QUIC
    368. RAIL
    369. Random Number Generator
    370. Raster image
    371. RDF
    372. Real User Monitoring (RUM)
    373. Recursion
    374. Reflow
    375. Regular expression
    376. Rendering engine
    377. Replay attack
    378. Repo
    379. Reporting directive
    380. Representation header
    381. Request header
    382. Resource Timing
    383. Response header
    384. Responsive web design
    385. REST
    386. RGB
    387. RIL
    388. Robots.txt
    389. Round Trip Time (RTT)
    390. Routers
    391. RSS
    392. Rsync
    393. RTCP (RTP Control Protocol)
    394. RTF
    395. RTL (Right to Left)
    396. RTP (Real-time Transport Protocol) and SRTP (Secure RTP)
    397. RTSP: Real-time streaming protocol
    398. Ruby
    399. Safe
    400. Same-origin policy
    401. SCM
    402. Scope
    403. Screen reader
    404. Script-supporting element
    405. Scroll container
    406. SCTP
    407. SDK (Software Development Kit)
    408. SDP
    409. Search engine
    410. Second-level Domain
    411. Secure Context
    412. Secure Sockets Layer (SSL)
    413. Selector (CSS)
    414. Self-Executing Anonymous Function
    415. Semantics
    416. SEO
    417. Serializable object
    418. Serialization
    419. Server
    420. Server Timing
    421. Session Hijacking
    422. SGML
    423. Shadow tree
    424. Shallow copy
    425. Shim
    426. Signature
    427. SIMD
    428. Simple header
    429. Simple response header
    430. SISD
    431. Site
    432. Site map
    433. SLD
    434. Sloppy mode
    435. Slug
    436. Smoke Test
    437. SMPTE (Society of Motion Picture and Television Engineers)
    438. SMTP
    439. Snap positions
    440. SOAP
    441. SPA (Single-page application)
    442. Specification
    443. Speculative parsing
    444. Speed index
    445. SQL
    446. SQL Injection
    447. SRI
    448. Stacking context
    449. State machine
    450. Statement
    451. Static method
    452. Static typing
    453. Sticky activation
    454. Strict mode
    455. String
    456. Stringifier
    457. STUN
    458. Style origin
    459. Stylesheet
    460. Submit button
    461. SVG
    462. SVN
    463. Symmetric-key cryptography
    464. Synchronous
    465. Syntax
    466. Syntax error
    467. Synthetic monitoring
    468. Table Grid Box
    469. Table Wrapper Box
    470. Tag
    471. TCP
    472. TCP handshake
    473. TCP slow start
    474. Telnet
    475. Texel
    476. The Khronos Group
    477. Thread
    478. Three js
    479. Time to first byte
    480. Time to interactive
    481. TLD
    482. TOFU
    483. Top layer
    484. Transient activation
    485. Transport Layer Security (TLS)
    486. Tree shaking
    487. Trident
    488. Truthy
    489. TTL
    490. TURN
    491. Type
    492. Type coercion
    493. Type conversion
    494. UDP (User Datagram Protocol)
    495. UI
    496. Undefined
    497. Unicode
    498. Unix time
    499. URI
    500. URL
    501. URN
    502. Usenet
    503. User agent
    504. UTF-8
    505. UUID
    506. UX
    507. Validator
    508. Value
    509. Variable
    510. Vendor Prefix
    511. Viewport
    512. Visual Viewport
    513. Void element
    514. VoIP
    515. W3C
    516. WAI
    517. WCAG
    518. Web performance
    519. Web server
    520. Web standards
    521. WebAssembly
    522. WebDAV
    523. WebExtensions
    524. WebGL
    525. WebIDL
    526. WebKit
    527. WebM
    528. WebP
    529. WebRTC
    530. WebSockets
    531. WebVTT
    532. WHATWG
    533. Whitespace
    534. WindowProxy
    535. World Wide Web
    536. Wrapper
    537. XForms Deprecated
    538. XHTML
    539. XInclude
    540. XLink
    541. XML
    542. XMLHttpRequest (XHR)
    543. XPath
    544. XQuery
    545. XSLT

Nullish value

In JavaScript, a nullish value is the value which is either null or undefined. Nullish values are always falsy.

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This page was last modified on Jun 8, 2023 by MDN contributors.

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