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Array

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Exercises (226)

○Array.from() — convert a string to chars
Beginner
○Array() — create an empty array
Beginner
○Array() — create array with a given length
Beginner
○Array() — create array from multiple arguments
Beginner
○Array() — create an array of zeros
Intermediate
○Array() — create a range [1…n]
Intermediate
○Array[Symbol.species] — subclass map()
Advanced
○Array[Symbol.species] — subclass filter()
Advanced
○Array[Symbol.species] — override to return plain Array
Advanced
○Array[Symbol.species] — subclass concat()
Advanced
○Array[Symbol.species] — Array.isArray on subclass result
Advanced
○Array.from() — create an index array
Beginner
○Array.from() — deduplicate with a Set
Intermediate
○Array.from() — generate even numbers with a map function
Intermediate
○Array.from() — count Unicode code points
Intermediate
○Array.from() — sum variadic arguments
Advanced
○Array.fromAsync() — resolve an array of promises
Advanced
○Array.fromAsync() — collect from a generator
Advanced
○Array.fromAsync() — map each element
Advanced
○Array.fromAsync() — works with sync iterables
Advanced
○Array.fromAsync() — safe collection with fallback
Advanced
○Array.isArray() — basic check
Beginner
○Array.isArray() — why not typeof
Beginner
○Array.isArray() — filter only arrays
Intermediate
○Array.isArray() — check if all elements are arrays
Intermediate
○Array.isArray() — distinguish array-like objects
Advanced
○Array.of() — create an array from arguments
Beginner
○Array.of() — avoid the single-number trap
Beginner
○Array.of() — wrap a single value
Beginner
○Array.of() — mixed-type array
Intermediate
○Array.of() — verify deep equality
Intermediate
○Array.prototype.at() — get first element
Beginner
○Array.prototype.at() — get last element
Beginner
○Array.prototype.at() — second-to-last element
Beginner
○Array.prototype.at() — out-of-bounds returns undefined
Intermediate
○Array.prototype.at() — get middle element
Intermediate
○Array.prototype.concat() — join two arrays
Beginner
○Array.prototype.concat() — join multiple arrays
Beginner
○Array.prototype.concat() — append a value
Beginner
○Array.prototype.concat() — immutability
Intermediate
○Array.prototype.concat() — merge three arrays
Intermediate
○Array.prototype.copyWithin() — copy to index
Intermediate
○Array.prototype.copyWithin() — shift elements left
Intermediate
○Array.prototype.copyWithin() — negative target index
Intermediate
○Array.prototype.copyWithin() — copy a range
Advanced
○Array.prototype.copyWithin() — returns the same array
Intermediate
○Array.prototype.entries() — convert to array
Beginner
○Array.prototype.entries() — index/value pairs
Intermediate
○Array.prototype.entries() — find entry by value
Intermediate
○Array.prototype.entries() — rebuild array from iterator
Intermediate
○Array.prototype.entries() — combine arrays into an object
Advanced
○Array.prototype.every() — check all positive
Beginner
○Array.prototype.every() — check non-empty strings
Beginner
○Array.prototype.every() — vacuous truth
Beginner
○Array.prototype.every() — check object properties
Intermediate
○Array.prototype.every() — check all even
Intermediate
○Array.prototype.fill() — fill entire array
Beginner
○Array.prototype.fill() — fill from index
Beginner
○Array.prototype.fill() — fill a range
Intermediate
○Array.prototype.fill() — create zero-filled array
Intermediate
○Array.prototype.fill() — fill last elements with negative index
Intermediate
○Array.prototype.filter() — keep even numbers
Beginner
○Array.prototype.filter() — filter by string length
Beginner
○Array.prototype.filter() — filter objects by property
Intermediate
○Array.prototype.filter() — keep unique values
Intermediate
○Array.prototype.filter() — remove falsy values
Intermediate
○Array.prototype.find() — find first match
Beginner
○Array.prototype.find() — find object by id
Intermediate
○Array.prototype.find() — returns undefined when not found
Beginner
○Array.prototype.find() — find string by length
Intermediate
○Array.prototype.find() — find in range
Intermediate
○Array.prototype.findIndex() — index of first match
Beginner
○Array.prototype.findIndex() — find object index by id
Intermediate
○Array.prototype.findIndex() — returns -1 when not found
Beginner
○Array.prototype.findIndex() — find string index by length
Intermediate
○Array.prototype.findIndex() — find by property vs reference
Advanced
○Array.prototype.findLast() — find last even number
Beginner
○Array.prototype.findLast() — last active user
Intermediate
○Array.prototype.findLast() — returns undefined when not found
Beginner
○Array.prototype.findLast() — last short string
Intermediate
○Array.prototype.findLast() — first vs last match
Intermediate
○Array.prototype.findLastIndex() — index of last even
Beginner
○Array.prototype.findLastIndex() — last active user index
Intermediate
○Array.prototype.findLastIndex() — returns -1 when not found
Beginner
○Array.prototype.findLastIndex() — last long string index
Intermediate
○Array.prototype.findLastIndex() — last duplicate index
Advanced
○Array.prototype.flat() — flatten one level
Beginner
○Array.prototype.flat() — flatten to any depth
Intermediate
○Array.prototype.flat() — flatten two levels
Intermediate
○Array.prototype.flat() — remove falsy and flat
Intermediate
○Array.prototype.flat() — configurable depth
Advanced
○Array.prototype.flatMap() — duplicate each element
Beginner
○Array.prototype.flatMap() — split sentences into words
Intermediate
○Array.prototype.flatMap() — double even numbers
Intermediate
○Array.prototype.flatMap() — expand ranges
Intermediate
○Array.prototype.flatMap() — compact strings
Advanced
○Array.prototype.forEach() — sum array elements
Beginner
○Array.prototype.forEach() — collect property values
Beginner
○Array.prototype.forEach() — mutate array in-place
Intermediate
○Array.prototype.forEach() — always returns undefined
Intermediate
○Array.prototype.forEach() — implement map manually
Intermediate
○Array.prototype.includes() — check for a value
Beginner
○Array.prototype.includes() — check for a word
Beginner
○Array.prototype.includes() — finding NaN
Intermediate
○Array.prototype.includes() — search from index
Intermediate
○Array.prototype.includes() — finding null
Intermediate
○Array.prototype.indexOf() — find first index
Beginner
○Array.prototype.indexOf() — returns -1 when not found
Beginner
○Array.prototype.indexOf() — find word index
Beginner
○Array.prototype.indexOf() — search from index
Intermediate
○Array.prototype.indexOf() — find first duplicate value
Intermediate
○Array.prototype.join() — join with comma-space
Beginner
○Array.prototype.join() — custom separator
Beginner
○Array.prototype.join() — build a file path
Intermediate
○Array.prototype.join() — default separator
Beginner
○Array.prototype.join() — build an HTML list
Intermediate
○Array.prototype.keys() — convert iterator to array
Beginner
○Array.prototype.keys() — count the keys
Beginner
○Array.prototype.keys() — keys over sparse arrays
Intermediate
○Array.prototype.keys() — iterate with for…of
Intermediate
○Array.prototype.keys() — build an index map
Advanced
○Array.prototype.lastIndexOf() — find last position
Beginner
○Array.prototype.lastIndexOf() — returns -1 when not found
Beginner
○Array.prototype.lastIndexOf() — search from a given index
Intermediate
○Array.prototype.lastIndexOf() — detect duplicate values
Intermediate
○Array.prototype.lastIndexOf() — collect all occurrences
Advanced
○Array.prototype.length — read the length
Beginner
○Array.prototype.length — empty array has length 0
Beginner
○Array.prototype.length — truncate by setting length
Intermediate
○Array.prototype.length — extend with sparse holes
Intermediate
○Array.prototype.length — length after pushing elements
Intermediate
○Array.prototype.map() — double each number
Beginner
○Array.prototype.map() — convert numbers to strings
Beginner
○Array.prototype.map() — pluck a property from objects
Intermediate
○Array.prototype.map() — use the index parameter
Intermediate
○Array.prototype.map() — parse strings to numbers
Intermediate
○Array.prototype.pop() — remove and return last element
Beginner
○Array.prototype.pop() — returns undefined for empty array
Beginner
○Array.prototype.pop() — verify array is mutated
Intermediate
○Array.prototype.pop() — implement a stack pop
Intermediate
○Array.prototype.pop() — remove the last word
Intermediate
○Array.prototype.push() — add to end
Beginner
○Array.prototype.push() — push multiple values
Beginner
○Array.prototype.push() — return value is the new length
Intermediate
○Array.prototype.push() — build an array with a loop
Intermediate
○Array.prototype.push() — collect evens with forEach
Intermediate
○Array.prototype.reduce() — sum all elements
Beginner
○Array.prototype.reduce() — product of all elements
Beginner
○Array.prototype.reduce() — flatten nested arrays
Intermediate
○Array.prototype.reduce() — count word occurrences
Intermediate
○Array.prototype.reduce() — find the maximum value
Intermediate
○Array.prototype.reduceRight() — sum from right
Beginner
○Array.prototype.reduceRight() — flatten from right
Intermediate
○Array.prototype.reduceRight() — join words in reverse order
Intermediate
○Array.prototype.reduceRight() — function composition
Advanced
○Array.prototype.reduceRight() — build a nested object
Advanced
○Array.prototype.reverse() — non-mutating reverse
Beginner
○Array.prototype.reverse() — reverse characters of a string
Beginner
○Array.prototype.reverse() — in-place mutation
Intermediate
○Array.prototype.reverse() — reverse word order in a sentence
Intermediate
○Array.prototype.reverse() — check if array is a palindrome
Advanced
○Array.prototype.shift() — remove and return the first element
Beginner
○Array.prototype.shift() — shifting an empty array
Beginner
○Array.prototype.shift() — mutation and same reference
Intermediate
○Array.prototype.shift() — dequeue from a queue
Intermediate
○Array.prototype.shift() — consume the first word
Intermediate
○Array.prototype.slice() — basic slice
Beginner
○Array.prototype.slice() — shallow copy
Beginner
○Array.prototype.slice() — last N elements
Intermediate
○Array.prototype.slice() — first N elements
Beginner
○Array.prototype.slice() — remove first and last
Intermediate
○Array.prototype.some() — check for negatives
Beginner
○Array.prototype.some() — long string check
Beginner
○Array.prototype.some() — empty array behaviour
Beginner
○Array.prototype.some() — find an admin user
Intermediate
○Array.prototype.some() — detect duplicates
Intermediate
○Array.prototype.sort() — alphabetical order
Beginner
○Array.prototype.sort() — numeric ascending
Beginner
○Array.prototype.sort() — numeric descending
Intermediate
○Array.prototype.sort() — sort objects by property
Intermediate
○Array.prototype.sort() — stable sort by last name
Advanced
○Array.prototype.splice() — remove an element
Beginner
○Array.prototype.splice() — insert an element
Intermediate
○Array.prototype.splice() — replace an element
Intermediate
○Array.prototype.splice() — capture removed elements
Intermediate
○Array.prototype.splice() — replace a range
Advanced
○Array.prototype.toReversed() — immutable reverse
Beginner
○Array.prototype.toReversed() — no mutation
Intermediate
○Array.prototype.toReversed() — reverse string array
Intermediate
○Array.prototype.toReversed() — new reference
Intermediate
○Array.prototype.toReversed() — empty array
Beginner
○Sort Array Immutably
Beginner
○toSorted Does Not Mutate
Intermediate
○Sort Strings Lexicographically
Beginner
○Sort by String Length
Intermediate
○toSorted Returns a New Reference
Intermediate
○Remove Element Immutably
Beginner
○Insert Element Immutably
Intermediate
○toSpliced Does Not Mutate
Intermediate
○Replace Element Immutably
Intermediate
○toSpliced Returns a New Array
Intermediate
○Convert Number Array to String
Beginner
○Convert String Array to String
Beginner
○toString Equals join with Comma
Intermediate
○toString with Nested Arrays
Intermediate
○toString of Empty Array
Beginner
○Add Element to Start of Array
Beginner
○Prepend Multiple Elements
Beginner
○unshift Returns the New Length
Intermediate
○unshift Mutates the Array
Intermediate
○Implement a Queue with unshift
Intermediate
○Get Array Values as Array
Beginner
○Iterate with values()
Beginner
○Compare values() and keys()
Intermediate
○Spread an Array Values Iterator
Intermediate
○values() Is the Default Iterator
Advanced
○Replace Element at Index
Beginner
○Replace Last Element
Intermediate
○Verify No Mutation
Intermediate
○Confirm New Array Reference
Intermediate
○Apply Multiple Replacements
Advanced
○Localize a Number Array
Beginner
○Format Amounts as Currency
Intermediate
○Format an Array of Dates
Intermediate
○Mixed Array toLocaleString
Intermediate
○Empty Array toLocaleString
Beginner