Array.map()
JavaScript Array.map() — Creates a new array by transforming each element.
Array.filter()
JavaScript Array.filter() — Keeps elements that pass a test.
Array.reduce()
JavaScript Array.reduce() — Reduces array to a single value.
Array.forEach()
JavaScript Array.forEach() — Executes callback for each element.
Array.find()
JavaScript Array.find() — Returns first matching element.
Array.findIndex()
JavaScript Array.findIndex() — Returns index of first match.
Array.some()
JavaScript Array.some() — True if any element passes test.
Array.every()
JavaScript Array.every() — True if all elements pass test.
Array.includes()
JavaScript Array.includes() — Checks if value exists.
Array.indexOf()
JavaScript Array.indexOf() — First index of value.
Array.slice()
JavaScript Array.slice() — Non-mutating subarray copy.
Array.concat()
JavaScript Array.concat() — Merge arrays.
Array.flat()
JavaScript Array.flat() — Flatten nested arrays.
Array.flatMap()
JavaScript Array.flatMap() — Map then flatten one level.
Array.sort()
JavaScript Array.sort() — Sorts array in place.
Array.reverse()
JavaScript Array.reverse() — Reverses array in place.
Array.splice()
JavaScript Array.splice() — Add/remove elements in place.
Array.toSorted()
JavaScript Array.toSorted() — Non-mutating sort (ES2023).
Array.at()
JavaScript Array.at() — Index with negative support.
Array.fill()
JavaScript Array.fill() — Fill range with value.
Array.copyWithin()
JavaScript Array.copyWithin() — Copy part of array within itself.
Array.entries()
JavaScript Array.entries() — Iterator of [index, value].
Array.keys()
JavaScript Array.keys() — Iterator of indices.
Array.values()
JavaScript Array.values() — Iterator of values.
Array.from()
JavaScript Array.from() — Create array from iterable.
Array.of()
JavaScript Array.of() — Create array from arguments.
Array.isArray()
JavaScript Array.isArray() — Check if value is array.
String.charAt()
JavaScript String.charAt() — Character at index.
String.charCodeAt()
JavaScript String.charCodeAt() — UTF-16 code unit.
String.slice()
JavaScript String.slice() — Extract substring.
String.substring()
JavaScript String.substring() — Extract between indices.
String.substr()
JavaScript String.substr() — Legacy substring by length.
String.indexOf()
JavaScript String.indexOf() — First index of substring.
String.lastIndexOf()
JavaScript String.lastIndexOf() — Last index of substring.
String.includes()
JavaScript String.includes() — Check substring exists.
String.startsWith()
JavaScript String.startsWith() — Prefix test.
String.endsWith()
JavaScript String.endsWith() — Suffix test.
String.trim()
JavaScript String.trim() — Remove whitespace both ends.
String.trimStart()
JavaScript String.trimStart() — Remove leading whitespace.
String.trimEnd()
JavaScript String.trimEnd() — Remove trailing whitespace.
String.toLowerCase()
JavaScript String.toLowerCase() — Lowercase copy.
String.toUpperCase()
JavaScript String.toUpperCase() — Uppercase copy.
String.replace()
JavaScript String.replace() — Replace first match.
String.replaceAll()
JavaScript String.replaceAll() — Replace all matches.
String.split()
JavaScript String.split() — Split to array.
String.padStart()
JavaScript String.padStart() — Pad start to length.
String.padEnd()
JavaScript String.padEnd() — Pad end to length.
String.repeat()
JavaScript String.repeat() — Repeat string.
String.match()
JavaScript String.match() — Match with RegExp.
String.matchAll()
JavaScript String.matchAll() — All matches iterator.
String.search()
JavaScript String.search() — Index of RegExp match.
String.localeCompare()
JavaScript String.localeCompare() — Locale-aware compare.