JavaScript Methods
Interactive Learning

constructor Makes a new empty array.

constructor Makes a new array filled with the elements you pass in.

constructor Makes a sparse array with empty slots.

constructor Makes a String object (primitive when not using new).

constructor Makes an empty object (equivalent to `{}`).

constructor Makes an object wrapping the given primitive value (e.g., string, number) or returns the value if already an object.

constructor Makes a Number object with the value `0` (primitive `0` when not using `new`).

constructor Makes a Number object from the given value (e.g., string, boolean), converting it to its numeric representation (primitive when not using `new`; returns `NaN` for invalid inputs).

constructor Makes a Date object representing the current date and time (in the local timezone).

constructor Makes a Date object from the given value: a string (parsed as a date), number of milliseconds since Unix epoch, or components (year, month, day, etc.).

constructor Makes a Date object with the given components (month is 0-based; uses local timezone).

constructor Makes a RegExp object that matches an empty string (equivalent to `/(?:)/`).

constructor Makes a RegExp object using the given pattern (as a string or another RegExp) and optional flags (e.g., "gi" for global and case-insensitive).

constructor Makes an empty Map object.

constructor Makes a Map object populated with key-value pairs from the given iterable (e.g., array of [key, value] arrays, or another Map/Set).

constructor Makes an empty Set object.

constructor Makes a Set object populated with the unique values from the given iterable (e.g., array, string, or another Set/Map).

constructor Makes a Boolean object with the value false (primitive false when not using new).

constructor Makes a Boolean object from the given value, converting it to its boolean representation via truthiness (falsy values like 0, "", null become false; others true; primitive when not using new).

constructor Makes a Promise object, which represents an asynchronous operation. The executor function receives two arguments: resolve (to fulfill the promise with a value) and reject (to reject with a reason). The executor runs immediately.

static Checks if something is an array.

static Converts things like strings or array-like objects into real arrays. You can also transform each item and set the `this` value for your transform function.

static Makes an array with whatever elements you pass in, no matter how many or what type.

static Makes a string from the given sequence of UTF-16 code units.

static Makes a string from the given sequence of code points.

static Returns the raw string form of a template literal.

static Copies enumerable properties from source objects to a target object, overwriting duplicates (shallow copy; changes the target).

static Makes an object with the given prototype object and optional property descriptors.

static Defines a new or modifies an existing property on the object with the given descriptor.

static Defines or modifies multiple properties on the object using an object of property descriptors.

static Returns an array of key-value pairs (arrays of [key, value]) for the enumerable properties of the object.

static Freezes the object, preventing new properties from being added and making existing properties non-writable and non-configurable (shallow freeze).

static Makes an object from an iterable of key-value pairs (e.g., from Array.entries() or Map.entries()).

static Gets the property descriptor for the given own property of the object (or undefined if not found).

static Returns an object containing all own property descriptors of the object.

static Returns an array of all own property names (including non-enumerable and symbols) of the object.

static Returns an array of all own symbol properties of the object.

static Gets the prototype of the given object.

static Returns true/false showing if the object has the given property as its own (not inherited).

static Compares two values for exact equality, handling special cases like NaN (unlike strict equality `===`).

static Returns true/false showing if the object is extensible (can have new properties added).

static Returns true/false showing if the object is frozen.

static Returns true/false showing if the object is sealed.

static Returns an array of the object's own enumerable property names (keys).

static Prevents new properties from being added to the object (makes it non-extensible).

static Seals the object, preventing new properties from being added and making existing properties non-configurable (but still writable; shallow seal).

static Sets the prototype of the object to the given prototype object.

static Returns an array of the object's own enumerable property values.

static The smallest number greater than 1 that can be represented as an IEEE 754 double precision floating-point value (approximately 2.220446049250313e-16).

static The largest integer that can be safely represented without losing precision (2^53 - 1, or 9007199254740991).

static The largest positive representable number (approximately 1.7976931348623157e+308).

static The smallest integer that can be safely represented without losing precision (-(2^53 - 1), or -9007199254740991).

static The smallest positive representable number (approximately 5e-324).

static The special "Not a Number" value.

static The special negative infinite value (-∞).

static The special positive infinite value (+∞).

static Provides the Number prototype from which all Numbers inherit.

static Returns true/false showing if the given value is a finite number (not `NaN`, `+∞`, or `-∞`).

static Returns true/false showing if the given value is an integer.

static Returns true/false showing if the given value is `NaN` (does not coerce to number first, unlike global `isNaN`).

static Returns true/false showing if the given value is an integer safe for arithmetic operations (within `MAX_SAFE_INTEGER` and `MIN_SAFE_INTEGER`).

static Parses a string argument and returns a floating-point number (ignores trailing non-numeric characters; equivalent to global `parseFloat`).

static Parses a string argument and returns an integer in the given radix (base 2-36; ignores trailing non-numeric characters; equivalent to global `parseInt`).

static Gets the current timestamp as the number of milliseconds since the Unix epoch (January 1, 1970, 00:00:00 UTC).

static Parses a string representation of a date and gives you the number of milliseconds since the Unix epoch (implementation-dependent parsing).

static Gets the number of milliseconds since the Unix epoch for the given UTC date components (month is 0-based).

static Provides the RegExp prototype from which all RegExps inherit.

static The base of the natural logarithm (Euler's constant, approximately 2.718281828459045).

static The natural logarithm of 10 (approximately 2.302585092994046).

static The natural logarithm of 2 (approximately 0.6931471805599453).

static The base-10 logarithm of E (approximately 0.4342944819032518).

static The base-2 logarithm of E (approximately 1.4426950408889634).

static The ratio of a circle's circumference to its diameter (approximately 3.141592653589793).

static The square root of 1/2 (approximately 0.7071067811865476).

static The square root of 2 (approximately 1.4142135623730951).

static Gets the absolute value of the given number (removes the sign).

static Gets the arccosine (inverse cosine) of the given number (in radians, 0 to π).

static Gets the hyperbolic arccosine (inverse hyperbolic cosine) of the given number (in radians; value ≥ 1).

static Gets the arcsine (inverse sine) of the given number (in radians, -π/2 to π/2).

static Gets the hyperbolic arcsine (inverse hyperbolic sine) of the given number (in radians).

static Gets the arctangent (inverse tangent) of the given number (in radians, -π/2 to π/2).

static Gets the arctangent of the quotient y/x (in radians, -π to π), accounting for the correct quadrant based on signs of y and x.

static Gets the cube root of the given number.

static Gets the smallest integer greater than or equal to the given number (rounds up).

static Gets the number of leading zero bits in the 32-bit integer representation of the given number.

static Gets the cosine of the given number (in radians).

static Gets the hyperbolic cosine of the given number.

static Returns e^x, where x is the given number (Euler's number raised to the power).

static Gets the result of subtracting 1 from e^x (more precise for small x than `exp(x) - 1`).

static Gets the largest integer less than or equal to the given number (rounds down).

static Gets the nearest single-precision (32-bit) float representation of the given number.

static Gets the square root of the sum of squares of the given numbers (Euclidean distance; avoids overflow).

static Gets the 32-bit integer result of multiplying two numbers (as if both were 32-bit signed integers).

static Gets the natural logarithm (base e) of the given number (value > 0).

static Gets the base-10 logarithm of the given number (value > 0).

static Gets the natural logarithm of 1 + x (more precise for small x than `log(1 + x)`).

static Gets the base-2 logarithm of the given number (value > 0).

static Gets the largest of the given numbers (returns `NaN` if any argument is `NaN`).

static Gets the smallest of the given numbers (returns `NaN` if any argument is `NaN`).

static Gets the result of raising the base to the exponent power.

static Returns a pseudo-random number between 0 (inclusive) and 1 (exclusive).

static Gets the value rounded to the nearest integer (rounds to even in halfway cases, e.g., 0.5 → 0, 1.5 → 2).

static Gets the sign of the given number: -1 for negative, 0 for zero, 1 for positive, or -0 for negative zero.

static Gets the sine of the given number (in radians).

static Gets the hyperbolic sine of the given number.

static Gets the positive square root of the given number (value ≥ 0).

static Gets the tangent of the given number (in radians).

static Gets the hyperbolic tangent of the given number.

static Gets the integer part of the given number (truncates the decimal portion without rounding).

static Parses a JSON string into a JavaScript value (object, array, string, number, boolean, or null). Optionally uses a reviver function to transform values during parsing (called for each key-value pair, returning the value or undefined to remove).

static Converts a JavaScript value to a JSON string. Optionally uses a replacer function (or array of keys) to filter/transform properties during serialization, and a space value (number for indentation, string for padding) for formatting.

static Returns one promise that resolves when all promises in the iterable resolve (array of results in order), or rejects with the first rejection reason (non-short-circuiting in ES2020+ with allSettled).

static Returns one promise that resolves with an array of objects describing the outcome of each promise ({status: "fulfilled" or "rejected", value or reason}).

static Returns one promise that resolves with the first fulfilled promise's value, or rejects with an AggregateError if all reject (short-circuiting on first success).

static Returns one promise that settles (resolves or rejects) with the first promise to settle, using its value or reason.

static Returns a promise that is rejected with the given reason (useful for immediate rejection).

static Returns a promise that is resolved with the given value (converts non-Promises to resolved Promises; useful for immediate fulfillment).

instance Gets the element at the index (supports negative indices for counting from the end).

instance Combines the array with one or more other arrays or values, returns a new array without modifying it.

instance Copies a sequence of elements within the Array to a new position, overwriting existing elements (changes the original).

instance Returns an Array Iterator object for iterating over key/value pairs (indices as keys, elements as values).

instance Checks if all elements pass the given testing function (returns a boolean).

instance Fills all or part of the array with a static value, from a start index to (but not including) an end index (changes the original).

instance Makes an array with elements that pass the given filtering function (optionally with a `this` value).

instance Gets the first element matching the given testing function (or `undefined` if none).

instance Gets the index of the first element matching the given testing function (or -1 if none).

instance Gets the last element matching the given testing function (or `undefined` if none; ES2023).

instance Gets the index of the last element matching the given testing function (or -1 if none; ES2023).

instance Makes an array with all sub-array elements concatenated into it, up to a certain depth (defaults to 1).

instance Maps every element using a mapping function and flattens the results into a new Array (equivalent to `map().flat()`; depth is always 1).

instance Runs a given function once for each Array element (mutates nothing; useful for side effects).

instance Checks if the Array contains a given value, starting from an optional index (returns a boolean).

instance Gets the first index at which a given element can be found (or -1 if not present; searches from an optional index).

instance Joins every element into a string, separated by the given string (defaults to comma).

instance Returns an Array Iterator object for iterating over the indices.

instance Gets the last index at which a given element can be found (or -1 if not present; searches backward from an optional index).

instance Makes an array with the results of calling a given function on every element (optionally with a `this` value).

instance Takes off the last element from the Array and gives it back (changes the original; returns `undefined` if empty).

instance Adds elements to the end and gives you the new length (changes the original).

instance Runs a function against an accumulator and every element (from left to right) to boil the array down to one value (optionally with an initial value).

instance Runs a function against an accumulator and every element (from right to left) to boil the array down to one value (optionally with an initial value).

instance Reverses elements directly (changes the original; returns the reversed Array).

instance Takes off the first element from the Array and gives it back (changes the original; returns `undefined` if empty).

instance Returns a shallow copy of a portion (from start to, but not including, end; negative indices supported).

instance Checks if at least one element passes the given testing function (returns a boolean).

instance Sorts the elements directly and gives you the sorted Array (changes the original; defaults to string lexicographic order).

instance Adds/removes elements from the Array at an index and gives you the deleted elements as a new Array (changes the original).

instance Returns a Array with elements in reversed order (immutable; ES2023).

instance Returns a Array with elements sorted (immutable; uses the given comparator or defaults to string order; ES2023).

instance Returns a Array with elements added/removed as per splice logic (immutable; ES2023).

instance Adds elements to the beginning and gives you the new length (changes the original).

instance Returns an Array Iterator object for iterating over the values.

instance Returns a Array with the element at the index replaced (immutable; ES2023).

instance Gets the character (exactly one UTF-16 code unit) at the index. Accepts negative integers, counting back from the last character.

instance Gets the character at the index.

instance Returns an integer between 0 and 65535 representing the UTF-16 code unit at the index.

instance Returns the Unicode code point value at the position (a non-negative integer).

instance Concatenates the string arguments to the calling string and returns a new string.

instance Checks if a string ends with the characters of a given string.

instance Checks if one string may be found within another string.

instance Gets the index of the first occurrence of the given value in the string.

instance Returns true/false showing if this string contains any lone surrogates.

instance Gets the index of the last occurrence of the given value in the string.

instance Returns a number showing if a reference string comes before, or after, or is the same as the given string in sort order.

instance Retrieves the result of matching a string against a regular expression.

instance Returns an iterator of all results matching a string against a regular expression, including capturing groups.

instance Gets the Unicode Normalization Form of the string.

instance Pads the current string with a given string (repeated, if needed) so that the resulting string reaches a given length.

instance Pads the current string with another string (multiple times, if needed) until the resulting string reaches the given length.

instance Constructs and returns a new string which contains the given number of copies of the string on which it was called.

instance Returns a string with one, some, or all matches of a pattern replaced by a replacement.

instance Returns a string with all matches of a pattern replaced by a replacement.

instance Searches for a match between a regular expression and the string.

instance Extracts a section of a string and gives it back as a new string, without modifying the original string.

instance Divides a String into an ordered list of substrings, puts these substrings into an array, and gives you the array.

instance Checks if a string begins with the characters of a given string.

instance Gets the part of the string between the start and end indexes, or to the end of the string.

instance Gets the calling string value converted to lower case, according to any locale-specific case mappings.

instance Gets the calling string value converted to upper case, according to any locale-specific case mappings.

instance Gets the calling string value converted to lower case.

instance Returns a string representing the given object.

instance Gets the calling string value converted to upper case.

instance Returns a string where all lone surrogates of this string are replaced with the Unicode replacement character U+FFFD.

instance Removes whitespace from both ends of a string and returns a new string, without modifying the original string.

instance Removes whitespace from the end of a string and returns a new string, without modifying the original string.

instance Removes whitespace from the beginning of a string and returns a new string, without modifying the original string.

instance Gets the primitive value of a String object.

instance Returns an Iterator object for iterating over the code points of the string, returning each code point as a string value.

instance Returns true/false showing if the object has the given property as its own (ignores the prototype chain).

instance Returns true/false showing if the object is in the prototype chain of the given object.

instance Returns true/false showing if the given property is enumerable.

instance Returns a locale-specific string representation of the object.

instance Returns a string representation of the object.

instance Gets the primitive value of the object.

instance Customizes the `instanceof` operator by defining how to check if an object is an instance of a constructor.

instance Determines if the object should be flattened when used with `Array.prototype.concat`.

instance Returns an iterator for iterating over the object's values.

instance Customizes the behavior of `String.prototype.match` when the object is used as a RegExp-like matcher.

instance Customizes the behavior of `String.prototype.replace` when the object is used as a RegExp-like replacer.

instance Customizes the behavior of `String.prototype.search` when the object is used as a RegExp-like searcher.

instance Specifies a constructor to use for derived objects.

instance Customizes the behavior of `String.prototype.split` when the object is used as a RegExp-like splitter.

instance Returns a primitive value representation of the object, given a hint.

instance Provides a string tag for the object, used in `toString`.

instance Returns an object whose properties are excluded from the `with` environment bindings.

instance Returns a string representing the number in exponential notation (e.g., "1.23e+4"), with an optional number of fraction digits (0-20).

instance Returns a string representing the number with a fixed number of decimal places (0-20; rounds as needed).

instance Returns a locale-specific string representation of the number (e.g., formatted with commas or currency symbols).

instance Returns a string representing the number to the given precision (significant digits, 1-21; uses fixed or exponential notation as appropriate).

instance Returns a string representation of the number in the given radix (base 2-36; defaults to base 10).

instance Gets the primitive number value of the Number object.

instance Gets the day of the month (1-31) for the date.

instance Gets the day of the week (0-6, where 0 is Sunday) for the date.

instance Gets the four-digit year for the date.

instance Gets the hour (0-23) for the date.

instance Gets the milliseconds (0-999) for the date.

instance Gets the minutes (0-59) for the date.

instance Gets the month (0-11) for the date.

instance Gets the seconds (0-59) for the date.

instance Gets the number of milliseconds since the Unix epoch for the date.

instance Gets the time zone difference in minutes from UTC for the date.

instance Gets the day of the month (1-31) for the UTC date.

instance Gets the day of the week (0-6) for the UTC date.

instance Gets the four-digit year for the UTC date.

instance Gets the hour (0-23) for the UTC date.

instance Gets the milliseconds (0-999) for the UTC date.

instance Gets the minutes (0-59) for the UTC date.

instance Gets the month (0-11) for the UTC date.

instance Gets the seconds (0-59) for the UTC date.

instance Sets the day of the month for the date and gives you the new timestamp (adjusts month/year if needed).

instance Sets the year (and optional month/day) for the date and gives you the new timestamp.

instance Sets the hours (and optional minutes/seconds/milliseconds) for the date and gives you the new timestamp (adjusts day if needed).

instance Sets the milliseconds for the date and gives you the new timestamp.

instance Sets the minutes (and optional seconds/milliseconds) for the date and gives you the new timestamp.

instance Sets the month (and optional day) for the date and gives you the new timestamp (adjusts year if needed).

instance Sets the seconds (and optional milliseconds) for the date and gives you the new timestamp.

instance Sets the date to the given timestamp (milliseconds since epoch) and gives you the new timestamp.

instance Sets the UTC day of the month for the date and gives you the new timestamp.

instance Sets the UTC year (and optional month/day) for the date and gives you the new timestamp.

instance Sets the UTC hours (and optional minutes/seconds/milliseconds) for the date and gives you the new timestamp.

instance Sets the UTC milliseconds for the date and gives you the new timestamp.

instance Sets the UTC minutes (and optional seconds/milliseconds) for the date and gives you the new timestamp.

instance Sets the UTC month (and optional day) for the date and gives you the new timestamp.

instance Sets the UTC seconds (and optional milliseconds) for the date and gives you the new timestamp.

instance Returns a string representing the date portion in the local timezone (e.g., "Tue Nov 21 2023").

instance Returns a string representing the date in ISO 8601 format (UTC, e.g., "2023-11-21T12:34:56.789Z").

instance Returns a JSON-safe string representation of the date (equivalent to `toISOString()` for serialization).

instance Returns a locale-specific string representing the date portion (e.g., "11/21/2023" in en-US).

instance Returns a locale-specific string representing the full date and time.

instance Returns a locale-specific string representing the time portion (e.g., "12:34:56 PM").

instance Returns a string representing the full date and time in the local timezone (implementation-dependent format).

instance Returns a string representing the time portion in the local timezone (e.g., "12:34:56 GMT-0500 (EST)").

instance Returns a string representing the date in UTC (RFC 1123 format, e.g., "Tue, 21 Nov 2023 17:34:56 GMT").

instance Gets the primitive timestamp value (milliseconds since epoch) of the Date object (same as `getTime()`).

instance A boolean showing if the dot (`.`) matches newlines (`s` flag).

instance A string with the flags of the RegExp (e.g., "gi").

instance A boolean showing if the `g` flag is set (matches all occurrences).

instance A boolean showing if the `d` flag is set (provides match indices; ES2024).

instance A boolean showing if the `i` flag is set (case-insensitive matching).

instance The index where to start the next match (used with global or sticky; writable).

instance A boolean showing if the `m` flag is set (treats `^` and `$` as line boundaries).

instance The source pattern of the RegExp (as a string, escaped for literal use).

instance A boolean showing if the `y` flag is set (matches starting at `lastIndex` only).

instance A boolean showing if the `u` flag is set (enables Unicode features like full code point support).

instance Customizes the behavior when the RegExp is used with `String.prototype.match` (returns matches or null).

instance Customizes the behavior when the RegExp is used with `String.prototype.matchAll` (returns an iterator of matches).

instance Customizes the behavior when the RegExp is used with `String.prototype.replace` (replaces matches).

instance Customizes the behavior when the RegExp is used with `String.prototype.search` (returns index of first match).

instance Customizes the behavior when the RegExp is used with `String.prototype.split` (splits on matches).

instance Executes the RegExp on the given string, returning an array of match details (including groups and index) or null; advances `lastIndex` if global.

instance Tests the string against the RegExp, returning true if there is a match or false otherwise; advances `lastIndex` if global.

instance Returns a string representation of the RegExp (e.g., `/pattern/flags`).

instance A read-only property representing the number of key-value pairs in the Map.

instance Removes all key-value pairs from the Map (changes the original).

instance Takes off the given key and its value from the Map (returns `true` if successful, `false` if key not found; mutates the original).

instance Runs a given function once for each key-value pair (callback receives value, key, and Map as arguments; optionally with a `this` value).

instance Gets the value associated with the given key, or `undefined` if the key doesn't exist.

instance Returns true/false showing if the Map contains the given key.

instance Returns an Iterator object for iterating over the keys in the order they were added.

instance Adds or updates the key-value pair in the Map and gives you the Map itself (mutates original; allows any type as key, including objects).

instance Returns an Iterator object for iterating over the values in the order they were added.

instance Returns an Iterator object for iterating over key-value pairs in the order they were added.

instance Returns an Iterator object for iterating over key-value pairs in the order they were added (lets you use `for...of` loops and destructuring).

instance Gets the string "Map" for the Map (used in `toString` and `instanceof`).

instance A read-only property representing the number of values in the Set.

instance Appends the given value to the Set (if not already present) and gives you the Set itself (mutates original; duplicates are ignored).

instance Removes all values from the Set (changes the original).

instance Takes off the given value from the Set (returns `true` if successful, `false` if value not found; mutates the original).

instance Runs a given function once for each value (callback receives value, same value as key, and Set as arguments; optionally with a `this` value).

instance Returns true/false showing if the Set contains the given value.

instance Returns an Iterator object for iterating over the values in the order they were added (identical to `values()` for Sets).

instance Returns an Iterator object for iterating over the values in the order they were added.

instance Returns an Iterator object for iterating over [value, value] pairs in the order they were added (for compatibility with Map).

instance Returns an Iterator object for iterating over the values in the order they were added (lets you use `for...of` loops and destructuring).

instance Gets the string "Set" for the Set (used in `toString` and `instanceof`).

instance Gets the string representation of the Boolean: "true" or "false".

instance Gets the primitive boolean value of the Boolean object (true or false).

instance Returns a promise and attaches a rejection handler (equivalent to .then(undefined, onRejectedHandler); catches errors).

instance Returns a promise that runs the handler after the promise settles (no matter what outcome), then resolves/rejects with the original value/reason (non-throwing; useful for cleanup).

instance Returns a promise and attaches handlers for when fulfilled or rejected. The new Promise resolves with the return value of the handler (or propagates rejection).