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Object

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Exercises (150)

○Object() — create empty object
Beginner
○Object() — wrap a primitive value
Beginner
○Object(null) — returns empty object
Beginner
○Object(undefined) — returns empty object
Beginner
○Object(obj) — returns the same reference
Intermediate
○Object.assign() — merge two objects
Beginner
○Object.assign() — multiple sources
Beginner
○Object.assign() — shallow clone
Beginner
○Object.assign() — apply defaults
Intermediate
○Object.assign() — return value is the target
Beginner
○Object.create() — create with prototype
Beginner
○Object.create() — access inherited methods
Intermediate
○Object.create(null) — no prototype
Intermediate
○Object.create() — inherited property access
Intermediate
○Object.create() — verify with getPrototypeOf
Intermediate
○Object.defineProperties() — define multiple at once
Beginner
○Object.defineProperties() — non-writable property
Intermediate
○Object.defineProperties() — non-enumerable property
Intermediate
○Object.defineProperties() — configurable: false prevents deletion
Advanced
○Object.defineProperties() — value and writable together
Intermediate
○Object.defineProperty() — define a value property
Beginner
○Object.defineProperty() — non-writable property
Intermediate
○Object.defineProperty() — non-enumerable property
Intermediate
○Object.defineProperty() — getter descriptor
Advanced
○Object.defineProperty() — configurable: false
Advanced
○Object.entries() — basic key-value pairs
Beginner
○Object.entries() — only own enumerable properties
Beginner
○Object.entries() — string values
Intermediate
○Object.entries() — order matches Object.keys
Beginner
○Object.entries() — convert object to Map
Intermediate
○Object.freeze() — prevent modification
Beginner
○Object.freeze() — Object.isFrozen returns true
Beginner
○Object.freeze() — returns same reference
Beginner
○Object.freeze() — shallow (nested objects not frozen)
Intermediate
○Object.freeze() — adding a property fails silently
Beginner
○Object.fromEntries() — array of pairs to object
Beginner
○Object.fromEntries() — Map to object
Beginner
○Object.fromEntries() — reverse of Object.entries
Beginner
○Object.fromEntries() — transform values
Intermediate
○Object.fromEntries() — empty iterable
Beginner
○Object.getOwnPropertyDescriptor() — basic descriptor
Beginner
○Object.getOwnPropertyDescriptor() — undefined for missing
Beginner
○Object.getOwnPropertyDescriptor() — getter descriptor
Intermediate
○Object.getOwnPropertyDescriptor() — inherited returns undefined
Intermediate
○Object.getOwnPropertyDescriptor() — check specific flags
Beginner
○Object.getOwnPropertyDescriptors() — get all descriptors
Beginner
○Object.getOwnPropertyDescriptors() — inspect all flags
Intermediate
○Object.getOwnPropertyDescriptors() — clone with Object.create
Intermediate
○Object.getOwnPropertyDescriptors() — includes non-enumerable
Intermediate
○Object.getOwnPropertyDescriptors() — Symbol properties separate
Intermediate
○Object.getOwnPropertyNames() — all own string keys
Beginner
○Object.getOwnPropertyNames() — vs Object.keys
Intermediate
○Object.getOwnPropertyNames() — empty object
Beginner
○Object.getOwnPropertyNames() — array-like includes length
Intermediate
○Object.getOwnPropertyNames() — inherited not included
Beginner
○Object.getOwnPropertySymbols() — returns Symbol keys
Intermediate
○Object.getOwnPropertySymbols() — empty when no symbols
Beginner
○Object.getOwnPropertySymbols() — Object.keys misses symbols
Beginner
○Object.getOwnPropertySymbols() — Symbol created with Symbol()
Beginner
○Object.getOwnPropertySymbols() — multiple symbols
Beginner
○Object.getPrototypeOf() — plain object prototype
Beginner
○Object.getPrototypeOf() — array prototype
Beginner
○Object.getPrototypeOf() — null prototype
Beginner
○Object.getPrototypeOf() — class instance prototype
Intermediate
○Object.getPrototypeOf() — function prototype
Intermediate
○Object.groupBy() — group by property value
Intermediate
○Object.groupBy() — group numbers by even/odd
Intermediate
○Object.groupBy() — group strings by length
Intermediate
○Object.groupBy() — empty array
Beginner
○Object.groupBy() — group by first letter
Intermediate
○Object.hasOwn() — own property returns true
Beginner
○Object.hasOwn() — missing property returns false
Beginner
○Object.hasOwn() — inherited property returns false
Intermediate
○Object.hasOwn() — vs hasOwnProperty
Intermediate
○Object.hasOwn() — works on null-prototype objects
Intermediate
○Object.is() — NaN equals NaN
Beginner
○Object.is() — distinguishes +0 from -0
Beginner
○Object.is() — same value returns true
Beginner
○Object.is() — different values return false
Beginner
○Object.is() — null equals null
Beginner
○Object.isExtensible() — plain object
Beginner
○Object.isExtensible() — after preventExtensions
Beginner
○Object.isExtensible() — after freeze
Intermediate
○Object.isExtensible() — after seal
Intermediate
○Object.isExtensible() — combining checks
Intermediate
○Object.isFrozen() — plain object
Beginner
○Object.isFrozen() — after Object.freeze
Beginner
○Object.isFrozen() — empty object after preventExtensions
Intermediate
○Object.isFrozen() — after seal (not frozen)
Intermediate
○Object.isFrozen() — deeply nested objects
Advanced
○Object.isSealed() — plain object
Beginner
○Object.isSealed() — after Object.seal
Beginner
○Object.isSealed() — after Object.freeze
Intermediate
○Object.isSealed() — empty non-extensible object
Intermediate
○Object.isSealed() — using in practice
Intermediate
○Object.keys() — basic usage
Beginner
○Object.keys() — inherited properties excluded
Beginner
○Object.keys() — non-enumerable properties
Intermediate
○Object.keys() — array-like objects
Beginner
○Object.keys() — counting and iterating
Beginner
○Object.preventExtensions() — basics
Beginner
○Object.preventExtensions() — verify with isExtensible
Beginner
○Object.preventExtensions() — existing props modifiable
Intermediate
○Object.preventExtensions() — prototype not affected
Intermediate
○Object.preventExtensions() — in strict mode throws
Intermediate
○Object.seal() — basics
Beginner
○Object.seal() — cannot delete properties
Beginner
○Object.seal() — writable properties remain writable
Intermediate
○Object.seal() — checking with isSealed
Beginner
○Object.seal() — returns the same object
Beginner
○Object.setPrototypeOf() — basics
Intermediate
○Object.setPrototypeOf() — set to null
Intermediate
○Object.setPrototypeOf() — verify with getPrototypeOf
Intermediate
○Object.setPrototypeOf() — inheritance chain
Advanced
○Object.setPrototypeOf() — returns the object
Beginner
○Object.values() — basic usage
Beginner
○Object.values() — insertion order
Beginner
○Object.values() — non-enumerable excluded
Intermediate
○Object.values() — inherited not included
Intermediate
○Object.values() — empty object
Beginner
○hasOwnProperty() — basics
Beginner
○hasOwnProperty() — vs inherited
Beginner
○hasOwnProperty() — inherited from Object.prototype
Intermediate
○hasOwnProperty() — after delete
Beginner
○hasOwnProperty() — safe null-prototype usage
Intermediate
○isPrototypeOf() — basics
Beginner
○isPrototypeOf() — deeper chain
Intermediate
○isPrototypeOf() — unrelated objects
Beginner
○isPrototypeOf() — null prototype
Intermediate
○isPrototypeOf() — vs instanceof
Intermediate
○propertyIsEnumerable() — basics
Beginner
○propertyIsEnumerable() — inherited property
Intermediate
○propertyIsEnumerable() — non-enumerable via defineProperty
Intermediate
○propertyIsEnumerable() — array indices
Beginner
○propertyIsEnumerable() — after defineProperty with enumerable:false
Advanced
○toLocaleString() — plain object default
Beginner
○toLocaleString() — number
Beginner
○toLocaleString() — custom override
Intermediate
○toLocaleString() — array delegation
Intermediate
○toLocaleString() — inherited from Object.prototype
Beginner
○toString() — plain object default
Beginner
○toString() — Object.prototype.toString.call(null)
Intermediate
○toString() — Object.prototype.toString.call([]) for arrays
Intermediate
○toString() — custom override
Intermediate
○toString() — Object.prototype.toString.call(42)
Intermediate
○valueOf() — plain object
Beginner
○valueOf() — Number valueOf
Beginner
○valueOf() — Boolean valueOf
Beginner
○valueOf() — custom valueOf override
Intermediate
○valueOf() — implicit conversion in arithmetic
Intermediate