JavaScript Methods /Functions

1. Array Methods:

array.length: Returns the number of elements in the array.
array.push(element): Adds one or more elements to the end of an array and returns the new length of the array.
array.pop(): Removes the last element from an array and returns that element.
array.shift(): Removes the first element from an array and returns it.
array.unshift(element): Adds one or more elements to the beginning of an array and returns the new length of the array.
array.slice(start, end): Returns a shallow copy of a portion of an array into a new array.
array.splice(start, deleteCount, item1, item2, ...): Adds/removes items to/from an array, starting at the given index.
array.indexOf(element): Returns the first index at which a given element can be found in the array, or -1 if it is not present.
array.includes(element): Determines whether an array contains a certain element, returning true or false.
array.sort(): Sorts the elements of an array in place and returns the sorted array.
array.reverse(): Reverses the order of the elements in an array.
array.forEach(callback): Executes a provided function once for each array element.
array.map(callback): Creates a new array populated with the results of calling a function for every array element.
array.filter(callback): Creates a new array with all elements that pass the test implemented by the provided function.
array.reduce(callback, initialValue): Applies a function against an accumulator and each element in the array to reduce it to a single value.
array.find(callback): Returns the first element in the array that satisfies the provided testing function.
array.findIndex(callback): Returns the index of the first element in the array that satisfies the provided testing function.
array.every(callback): Tests whether all elements in the array pass the provided function test.
array.some(callback): Tests whether at least one element in the array passes the provided function test.
array.concat(array2): Merges two or more arrays and returns a new array.
array.join(separator): Joins all elements of an array into a string.

2. String Methods:

string.length: Returns the length of a string.
string.toUpperCase(): Converts the string to uppercase.
string.toLowerCase(): Converts the string to lowercase.
string.charAt(index): Returns the character at the specified index.
string.indexOf(substring): Returns the index of the first occurrence of the specified substring, or -1 if not found.
string.lastIndexOf(substring): Returns the index of the last occurrence of the specified substring.
string.includes(substring): Determines whether a string contains another string, returning true or false.
string.slice(start, end): Extracts a section of a string and returns it as a new string.
string.split(separator): Splits a string into an array of substrings based on a specified separator.
string.trim(): Removes whitespace from both ends of a string.
string.replace(searchValue, newValue): Replaces a substring or pattern in the string with a new value.
string.startsWith(substring): Checks if the string starts with the specified substring.
string.endsWith(substring): Checks if the string ends with the specified substring.
string.repeat(count): Returns a new string with the original string repeated count times.

3. Object Methods:

Object.keys(obj): Returns an array of a given object's own property names.
Object.values(obj): Returns an array of a given object's own enumerable property values.
Object.entries(obj): Returns an array of a given object's own enumerable key-value pairs.
Object.assign(target, source): Copies all enumerable properties from one or more source objects to a target object.
Object.freeze(obj): Freezes an object, making it immutable.
Object.seal(obj): Seals an object, preventing new properties from being added but allowing modification of existing properties.
Object.hasOwnProperty(property): Returns true if the object has the specified property as its own property.

4. Number Methods:

Number.isNaN(value): Determines whether the value is NaN (Not-a-Number).
Number.isInteger(value): Determines whether the value is an integer.
Number.parseFloat(string): Converts a string to a floating-point number.
Number.parseInt(string): Converts a string to an integer.
number.toFixed(digits): Formats a number using fixed-point notation.
number.toString(base): Converts a number to a string, optionally using a specified base (radix).

5. Math Methods:

Math.round(value): Rounds a number to the nearest integer.
Math.floor(value): Rounds a number down to the nearest integer.
Math.ceil(value): Rounds a number up to the nearest integer.
Math.max(...values): Returns the largest of zero or more numbers.
Math.min(...values): Returns the smallest of zero or more numbers.
Math.random(): Returns a pseudo-random number between 0 and 1.
Math.abs(value): Returns the absolute value of a number.
Math.sqrt(value): Returns the square root of a number.
Math.pow(base, exponent): Returns the base to the exponent power (base^exponent).

6. Date Methods:

new Date(): Creates a new date object with the current date and time.
Date.now(): Returns the number of milliseconds since January 1, 1970.
date.getFullYear(): Returns the year of the specified date.
date.getMonth(): Returns the month (0-11) of the specified date.
date.getDate(): Returns the day of the month (1-31).
date.getDay(): Returns the day of the week (0-6).
date.getHours(): Returns the hour (0-23).
date.getMinutes(): Returns the minutes (0-59).
date.getSeconds(): Returns the seconds (0-59).
date.getMilliseconds(): Returns the milliseconds (0-999).

7. Control Flow Functions:

setTimeout(callback, delay): Executes the callback function after the specified delay (in milliseconds).
setInterval(callback, delay): Repeatedly executes the callback function after the specified delay (in milliseconds).
clearTimeout(id): Cancels a timeout previously established by setTimeout().
clearInterval(id): Cancels a repeated action set by setInterval().

8. Promise Methods:

Promise.all(iterable): Waits for all promises in the iterable to resolve or for any to reject.
Promise.race(iterable): Waits for the first promise to resolve or reject.
Promise.resolve(value): Returns a promise that is resolved with the given value.
Promise.reject(reason): Returns a promise that is rejected with the given reason.