#advancedjavascript — Public Fediverse posts
Live and recent posts from across the Fediverse tagged #advancedjavascript, aggregated by home.social.
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flatMap Can Filter AND Transform?!
flatMap is a SECRET WEAPON! Return empty array to REMOVE items, return array with value to KEEP. One pass does filter AND map together! This trick will make your code 10x cleaner!
#javascript #javascripttricks #flatmap #arrayfilter #arraytransformation #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascripttips #functionalprogramming #advancedjavascript
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Promise.resolve UNWRAPS Thenables?!
Promise.resolve has RECURSIVE unwrapping! Any object with a 'then' method gets called. Nested thenables unwrap ALL the way down until a real value appears. This automatic unwrapping will confuse your async code!
#javascript #javascripttricks #promise.resolve #thenables #asyncunwrapping #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #promisequirks #advancedjavascript
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Arrow Functions Have NO arguments?!
Arrow functions BREAK arguments! They don't have the arguments object. This will cause ReferenceError when you try to use it. Regular functions work, arrows don't!
#javascript #javascripttricks #arrowfunctions #argumentsobject #thisbinding #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #functiondifferences #advancedjavascript
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Reflect API Shows HIDDEN Properties?!
Reflect.ownKeys REVEALS secrets! It shows non-enumerable properties that Object.keys hides. This is how you see ALL properties, even hidden ones!
#javascript #javascripttricks #reflectapi #propertyenumeration #hiddenproperties #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #reflection #advancedjavascript
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Reflect API Shows HIDDEN Properties?!
Reflect.ownKeys REVEALS secrets! It shows non-enumerable properties that Object.keys hides. This is how you see ALL properties, even hidden ones!
#javascript #javascripttricks #reflectapi #propertyenumeration #hiddenproperties #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #reflection #advancedjavascript
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Constructor Can Return DIFFERENT Object?!
Constructors can LIE about what they create! If you return an object, it REPLACES the instance. The 'new' keyword becomes USELESS. instanceof returns false! This breaks OOP principles!
#javascript #javascripttricks #constructor #classsyntax #instanceof #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #oopquirks #advancedjavascript
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Constructor Can Return DIFFERENT Object?!
Constructors can LIE about what they create! If you return an object, it REPLACES the instance. The 'new' keyword becomes USELESS. instanceof returns false! This breaks OOP principles!
#javascript #javascripttricks #constructor #classsyntax #instanceof #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #oopquirks #advancedjavascript
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typeof Works in Temporal Dead Zone?!
Temporal Dead Zone has a LOOPHOLE! typeof works on undeclared variables (returns undefined) but throws ReferenceError for let/const. This inconsistency is INSANE!
#javascript #javascripttricks #tdz #temporaldeadzone #typeof #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #variablehoisting #advancedjavascript
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typeof Works in Temporal Dead Zone?!
Temporal Dead Zone has a LOOPHOLE! typeof works on undeclared variables (returns undefined) but throws ReferenceError for let/const. This inconsistency is INSANE!
#javascript #javascripttricks #tdz #temporaldeadzone #typeof #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #variablehoisting #advancedjavascript
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Object Keys Get AUTO-SORTED?!
Object key order is NOT guaranteed! Numeric string keys get SORTED before other keys. You add 'b' first but '1' appears first in Object.keys()! This auto-sorting will DESTROY your expected order!
#javascript #javascripttricks #object.keys #keyordering #numerickeys #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #objectquirks #advancedjavascript
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Object Keys Get AUTO-SORTED?!
Object key order is NOT guaranteed! Numeric string keys get SORTED before other keys. You add 'b' first but '1' appears first in Object.keys()! This auto-sorting will DESTROY your expected order!
#javascript #javascripttricks #object.keys #keyordering #numerickeys #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #objectquirks #advancedjavascript
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new Function() Ignores Local Scope?!
Function constructor is DANGEROUS! It always runs in GLOBAL scope, ignoring any variables in the enclosing function. Your local 'x' becomes invisible. This scoping behavior will cause HIDDEN bugs!
#javascript #javascripttricks #functionconstructor #globalscope #variablescope #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #scopequirks #advancedjavascript
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new Function() Ignores Local Scope?!
Function constructor is DANGEROUS! It always runs in GLOBAL scope, ignoring any variables in the enclosing function. Your local 'x' becomes invisible. This scoping behavior will cause HIDDEN bugs!
#javascript #javascripttricks #functionconstructor #globalscope #variablescope #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #scopequirks #advancedjavascript
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Tagged Template Does MATH in Strings?!
Tagged templates can EXECUTE CODE! The tag function receives values and can transform them. This one DOUBLES every number. String interpolation becomes code execution!
#javascript #javascripttricks #taggedtemplates #templateliterals #stringinterpolation #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #templateprocessing #advancedjavascript
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Tagged Template Does MATH in Strings?!
Tagged templates can EXECUTE CODE! The tag function receives values and can transform them. This one DOUBLES every number. String interpolation becomes code execution!
#javascript #javascripttricks #taggedtemplates #templateliterals #stringinterpolation #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #templateprocessing #advancedjavascript
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typeof Never Throws Error?!
typeof is INDESTRUCTIBLE! It works on undeclared variables WITHOUT throwing ReferenceError. Both declared undefined AND never-declared return 'undefined'. You can't tell them apart! This is INSANE!
#javascript #javascripttricks #typeof #undeclaredvariables #referenceerror #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #typechecking #advancedjavascript
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typeof Never Throws Error?!
typeof is INDESTRUCTIBLE! It works on undeclared variables WITHOUT throwing ReferenceError. Both declared undefined AND never-declared return 'undefined'. You can't tell them apart! This is INSANE!
#javascript #javascripttricks #typeof #undeclaredvariables #referenceerror #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #typechecking #advancedjavascript
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Spread Operator Works on STRINGS?!
Spread operator is MAGIC! It works on strings (splits to chars) but NOT on objects. This inconsistency will cause bugs when you least expect it!
#javascript #javascripttricks #spreadoperator #stringiteration #objectiteration #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #iterableprotocol #advancedjavascript
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Spread Operator Works on STRINGS?!
Spread operator is MAGIC! It works on strings (splits to chars) but NOT on objects. This inconsistency will cause bugs when you least expect it!
#javascript #javascripttricks #spreadoperator #stringiteration #objectiteration #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #iterableprotocol #advancedjavascript
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Nullish Coalescing vs Logical OR?!
?? and || are DIFFERENT! Nullish coalescing only checks null/undefined. Logical OR checks ALL falsy values. 0 and '' behave differently! This matters!
#javascript #javascripttricks #nullishcoalescing #logicalor #falsyvalues #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #operatordifferences #advancedjavascript
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Nullish Coalescing vs Logical OR?!
?? and || are DIFFERENT! Nullish coalescing only checks null/undefined. Logical OR checks ALL falsy values. 0 and '' behave differently! This matters!
#javascript #javascripttricks #nullishcoalescing #logicalor #falsyvalues #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #operatordifferences #advancedjavascript
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Labels Can Break ANY Block?!
JavaScript has GOTO in disguise! Labels with break can exit ANY block, not just loops! This code jumps OUT of nested blocks instantly. Most developers have NEVER seen this syntax!
#javascript #javascripttricks #labels #breakstatement #controlflow #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #hiddenfeatures #advancedjavascript
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Labels Can Break ANY Block?!
JavaScript has GOTO in disguise! Labels with break can exit ANY block, not just loops! This code jumps OUT of nested blocks instantly. Most developers have NEVER seen this syntax!
#javascript #javascripttricks #labels #breakstatement #controlflow #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #hiddenfeatures #advancedjavascript
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Array Methods Work on NON-Arrays?!
Array methods are DECEPTIVE! They work on any object with length property. This object isn't an array, but map() works on it! JavaScript lies about types!
#javascript #javascripttricks #arraymethods #arraylikeobjects #typecoercion #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #ducktyping #advancedjavascript
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Array Methods Work on NON-Arrays?!
Array methods are DECEPTIVE! They work on any object with length property. This object isn't an array, but map() works on it! JavaScript lies about types!
#javascript #javascripttricks #arraymethods #arraylikeobjects #typecoercion #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #ducktyping #advancedjavascript
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String Primitives Have Methods But No Properties?!
Strings are DECEPTIVE! They have methods (auto-boxing) but you can't assign properties. Properties disappear immediately. This is primitive vs object confusion!
#javascript #javascripttricks #stringprimitives #autoboxing #propertyassignment #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #primitivetypes #advancedjavascript
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String Primitives Have Methods But No Properties?!
Strings are DECEPTIVE! They have methods (auto-boxing) but you can't assign properties. Properties disappear immediately. This is primitive vs object confusion!
#javascript #javascripttricks #stringprimitives #autoboxing #propertyassignment #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #primitivetypes #advancedjavascript
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Array Holes Are NOT undefined?!
MIND BLOWN! An empty slot in an array is NOT the same as undefined. The hole doesn't exist as a property! map() SKIPS holes but processes undefined. This invisible difference will break your code!
#javascript #javascripttricks #arrayholes #sparsearrays #undefined #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #arraymethods #advancedjavascript
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Array Holes Are NOT undefined?!
MIND BLOWN! An empty slot in an array is NOT the same as undefined. The hole doesn't exist as a property! map() SKIPS holes but processes undefined. This invisible difference will break your code!
#javascript #javascripttricks #arrayholes #sparsearrays #undefined #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #arraymethods #advancedjavascript
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Array.fill() Shares Same Reference?!
This is a TRAP! Array.fill() with an object puts the SAME object in every slot. Change one, change ALL! Every element points to the same memory location. This silent mutation will destroy your data!
#javascript #javascripttricks #array.fill #objectreference #mutationbugs #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #referencetypes #advancedjavascript
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Array.fill() Shares Same Reference?!
This is a TRAP! Array.fill() with an object puts the SAME object in every slot. Change one, change ALL! Every element points to the same memory location. This silent mutation will destroy your data!
#javascript #javascripttricks #array.fill #objectreference #mutationbugs #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #referencetypes #advancedjavascript
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void Operator ERASES Any Value?!
The void operator is JavaScript's BLACK HOLE! It takes ANY expression and returns undefined. Even when the function returns 42, void turns it into NOTHING! This ancient operator will confuse everyone!
#javascript #javascripttricks #voidoperator #undefined #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #operatorquirks #javascriptbugs #advancedjavascript
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void Operator ERASES Any Value?!
The void operator is JavaScript's BLACK HOLE! It takes ANY expression and returns undefined. Even when the function returns 42, void turns it into NOTHING! This ancient operator will confuse everyone!
#javascript #javascripttricks #voidoperator #undefined #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #operatorquirks #javascriptbugs #advancedjavascript
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RegExp lastIndex Mutates Global Matches?!
Global regex has MEMORY! The lastIndex property remembers where it stopped. Reset it to 0 and the same regex matches DIFFERENTLY. This mutation behavior will cause bugs you'll never find!
#javascript #javascripttricks #regexp #lastindex #globalregex #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #regexmutation #advancedjavascript
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RegExp lastIndex Mutates Global Matches?!
Global regex has MEMORY! The lastIndex property remembers where it stopped. Reset it to 0 and the same regex matches DIFFERENTLY. This mutation behavior will cause bugs you'll never find!
#javascript #javascripttricks #regexp #lastindex #globalregex #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #regexmutation #advancedjavascript
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WeakMap REJECTS Primitive Keys?!
WeakMap has a SECRET rule! It ONLY accepts objects as keys. Try to use a string and it FAILS silently. This hidden restriction will cause bugs you'll never find!
#javascript #javascripttricks #weakmap #objectkeys #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #weakreferences #javascriptbugs #advancedjavascript
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WeakMap REJECTS Primitive Keys?!
WeakMap has a SECRET rule! It ONLY accepts objects as keys. Try to use a string and it FAILS silently. This hidden restriction will cause bugs you'll never find!
#javascript #javascripttricks #weakmap #objectkeys #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #weakreferences #javascriptbugs #advancedjavascript
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Tagged Template Literals Have RAW Property?!
Template literals have a SECRET! The raw property shows escape sequences as LITERAL characters. \n becomes TWO characters, not one newline. This hidden feature will blow your mind!
#javascript #javascripttricks #templateliterals #taggedtemplates #rawproperty #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #stringescaping #advancedjavascript
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Tagged Template Literals Have RAW Property?!
Template literals have a SECRET! The raw property shows escape sequences as LITERAL characters. \n becomes TWO characters, not one newline. This hidden feature will blow your mind!
#javascript #javascripttricks #templateliterals #taggedtemplates #rawproperty #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #stringescaping #advancedjavascript
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Proxy Returns Function That Executes Itself?!
This Proxy BREAKS all rules! When you access ANY property, it returns a function that executes immediately. The property name becomes the function result. This is INSANE behavior that will break your brain!
#javascript #javascripttricks #proxy #gettrap #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #proxytraps #javascriptbugs #advancedjavascript
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Proxy Returns Function That Executes Itself?!
This Proxy BREAKS all rules! When you access ANY property, it returns a function that executes immediately. The property name becomes the function result. This is INSANE behavior that will break your brain!
#javascript #javascripttricks #proxy #gettrap #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #proxytraps #javascriptbugs #advancedjavascript
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Object.freeze Is SHALLOW?!
Object.freeze LIES about immutability! It only freezes the top level. Nested objects are STILL mutable! This shallow freeze will cause bugs!
#javascript #javascripttricks #object.freeze #shallowfreeze #immutability #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #objectmutation #advancedjavascript
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Object.freeze Is SHALLOW?!
Object.freeze LIES about immutability! It only freezes the top level. Nested objects are STILL mutable! This shallow freeze will cause bugs!
#javascript #javascripttricks #object.freeze #shallowfreeze #immutability #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #objectmutation #advancedjavascript
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Symbol.species Controls Constructor?!
Symbol.species is POWERFUL! It controls what constructor methods return. Your custom array methods return plain Array, not your subclass! This breaks inheritance!
#javascript #javascripttricks #symbol.species #constructorcontrol #subclassing #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #classinheritance #advancedjavascript
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Symbol.species Controls Constructor?!
Symbol.species is POWERFUL! It controls what constructor methods return. Your custom array methods return plain Array, not your subclass! This breaks inheritance!
#javascript #javascripttricks #symbol.species #constructorcontrol #subclassing #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #classinheritance #advancedjavascript
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Getter That Accesses ITSELF?!
This getter is RECURSIVE! It tries to access its own property, creating infinite recursion. But JavaScript handles it... somehow. This will break your brain!
#javascript #javascripttricks #object.defineproperty #circularreference #recursivegetter #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #propertydescriptors #advancedjavascript
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Getter That Accesses ITSELF?!
This getter is RECURSIVE! It tries to access its own property, creating infinite recursion. But JavaScript handles it... somehow. This will break your brain!
#javascript #javascripttricks #object.defineproperty #circularreference #recursivegetter #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #propertydescriptors #advancedjavascript
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Proxy Returns Itself Infinitely?!
This Proxy BREAKS reality! Every property access returns ANOTHER Proxy. You can access infinite nested properties and they ALL work. This is INSANE behavior that defies logic!
#javascript #javascripttricks #proxy #recursivetrap #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #infiniteproxy #javascriptbugs #advancedjavascript
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Proxy Returns Itself Infinitely?!
This Proxy BREAKS reality! Every property access returns ANOTHER Proxy. You can access infinite nested properties and they ALL work. This is INSANE behavior that defies logic!
#javascript #javascripttricks #proxy #recursivetrap #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #infiniteproxy #javascriptbugs #advancedjavascript
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Generator yield* Delegates to Another?!
Generators can DELEGATE to other generators! The yield* syntax passes control to another generator. This creates generator chains that will confuse you!
#javascript #javascripttricks #generators #yield* #delegation #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #generatorchains #advancedjavascript
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Generator yield* Delegates to Another?!
Generators can DELEGATE to other generators! The yield* syntax passes control to another generator. This creates generator chains that will confuse you!
#javascript #javascripttricks #generators #yield* #delegation #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #generatorchains #advancedjavascript
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Class Fields Initialize in ORDER?!
Class fields initialize SEQUENTIALLY! Field a tries to access field b BEFORE b is initialized. This creates undefined references that will confuse you!
#javascript #javascripttricks #classfields #initializationorder #undefinedreferences #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #classsyntax #advancedjavascript
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Class Fields Initialize in ORDER?!
Class fields initialize SEQUENTIALLY! Field a tries to access field b BEFORE b is initialized. This creates undefined references that will confuse you!
#javascript #javascripttricks #classfields #initializationorder #undefinedreferences #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #classsyntax #advancedjavascript
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Function.length Counts Parameters WRONG?!
Function.length LIES! It counts parameters, but stops at default values. Rest parameters don't count. This property is DECEPTIVE!
#javascript #javascripttricks #function.length #parametercounting #defaultparameters #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #functionmetadata #advancedjavascript
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Function.length Counts Parameters WRONG?!
Function.length LIES! It counts parameters, but stops at default values. Rest parameters don't count. This property is DECEPTIVE!
#javascript #javascripttricks #function.length #parametercounting #defaultparameters #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #functionmetadata #advancedjavascript
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Symbol.iterator Creates INFINITE Sequence?!
Custom iterators can generate INFINITE sequences! This object never ends, but spread operator can slice it. This is how generators break the rules of finite data!
#javascript #javascripttricks #symbol.iterator #generators #infinitesequences #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #iterators #advancedjavascript
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Symbol.iterator Creates INFINITE Sequence?!
Custom iterators can generate INFINITE sequences! This object never ends, but spread operator can slice it. This is how generators break the rules of finite data!
#javascript #javascripttricks #symbol.iterator #generators #infinitesequences #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #iterators #advancedjavascript
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Destructuring Defaults Are TRICKY?!
Destructuring defaults have LAYERS! Nested defaults work differently than you think. undefined triggers defaults, but missing properties don't! This is confusing!
#javascript #javascripttricks #destructuring #defaultvalues #nesteddestructuring #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #objectdestructuring #advancedjavascript
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Modifying Array.prototype Affects ALL Arrays?!
Array.prototype is GLOBAL! Adding methods affects EVERY array in your code. This global pollution will break other code. This is why you never modify prototypes!
#javascript #javascripttricks #array.prototype #prototypepollution #globalmodification #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #prototypechain #advancedjavascript
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Getter That MODIFIES Itself When Called?!
This getter is ALIVE! Every time you access it, it CHANGES its own behavior. First call returns one value, second call returns something completely different. This self-modifying code will break your logic!
#javascript #javascripttricks #getters #object.defineproperty #selfmodifyingcode #javascriptweird #javascriptquiz #codingchallenge #javascriptshorts #javascriptwtf #propertydescriptors #advancedjavascript