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Posted on Dec 9, 2023 • Edited on Mar 7, 2024

🚀 JavaScript Array, Object, and Map Methods Cheat sheet 🚀

#javascript #datastructures #programming #interview

Introduction 🌐

🌟 Welcome to this article, your go-to cheat sheet for essential array and object methods frequently applied in your work or personal projects. This guide ensures you're well-prepared for upcoming articles on implementing JavaScript data structures. Don't hesitate to comment if you spot any crucial methods I might have overlooked. Let's dive right in without any delay!

JavaScript Array Methods:

const nums = [1, 5, 11, 2, 55, 6];

at(): Retrieves the element at the specified index in the array.

const element = nums.at(2); // Returns the element at index 2: 11

concat(): Combines two or more arrays.

const newArray = nums.concat([7, 8, 9]); // Returns a new array: [1, 5, 11, 2, 55, 6, 7, 8, 9]

copyWithin(): Copies a sequence of elements within the array.

nums.copyWithin(0, 3, 5); // Copies elements from index 3 to 4 to the beginning: [2, 55, 11, 2, 55, 6]

entries(): Returns an iterator object for key/value pairs of the array.

const iterator = nums.entries();
for (const [index, value] of iterator) {
  console.log(index, value);
}
// Outputs:
// 0 1
// 1 5
// 2 11
// 3 2
// 4 55
// 5 6

every(): Checks if all elements in the array pass a certain condition.

const allGreaterThanZero = nums.every((num) => num > 0); // Returns true

fill(): Fills all elements of the array with a static value.

const filledArray = nums.fill(0); // Fills the array with 0: [0, 0, 0, 0, 0, 0]

filter(): Creates a new array with elements that pass a certain condition.

const evenNumbers = nums.filter((num) => num % 2 === 0); // Returns a new array: [2, 6]

find(): Returns the first element in the array that satisfies a given condition.

const greaterThanTen = nums.find((num) => num > 10); // Returns 11

findIndex(): Returns the index of the first element in the array that satisfies a given condition.

const indexGreaterThanTen = nums.findIndex((num) => num > 10); // Returns the index of 11: 2

flat(): Flattens nested arrays.

const nestedArray = [1, [2, 3], [4, [5, 6]]];
const flattenedArray = nestedArray.flat(); // Returns a new array: [1, 2, 3, 4, [5, 6]]

flatMap(): Maps each element using a function and flattens the result.

const doubledAndFlattened = nums.flatMap((num) => [num * 2]); // Returns a new array: [2, 10, 22, 4, 110, 12]

forEach(): Executes a provided function once for each array element.

nums.forEach((num) => console.log(num)); // Outputs each element in the array

from(): Creates a new array from an array-like or iterable object.

const newArrayFromSet = Array.from(new Set([1, 2, 2, 3])); // Returns a new array: [1, 2, 3]

includes(): Checks if an array includes a certain element.

const includesFive = nums.includes(5); // Returns true

indexOf(): Returns the first index at which a given element is found.

const indexofFive = nums.indexOf(5); // Returns the index of 5: 1

isArray(): Checks if a value is an array.

const isAnArray = Array.isArray(nums); // Returns true

join(): Joins all elements of an array into a string.

const joinedString = nums.join("-"); // Returns a string: "1-5-11-2-55-6"

keys(): Returns an iterator of keys in the array.

const keyIterator = nums.keys();
for (const key of keyIterator) {
  console.log(key);
}
// Outputs:
// 0
// 1
// 2
// 3
// 4
// 5

lastIndexOf(): Returns the last index at which a given element is found.

const lastIndexOfFive = nums.lastIndexOf(5); // Returns the last index of 5: 3

map(): Creates a new array with the results of calling a provided function on every element.

const squaredArray = nums.map((num) => num * num); // Returns a new array: [1, 25, 121, 4, 3025, 36]

pop(): Removes the last element from an array and returns that element.

const lastElement = nums.pop(); // Returns 6, and nums is now [1, 5, 11, 2, 55]

push(): Adds one or more elements to the end of an array and returns the new length.

const newLength = nums.push(7, 8); // Returns the new length: 7, and nums is now [1, 5, 11, 2, 55, 7, 8]

reduce(): Reduces the array to a single value using a provided function.

const sum = nums.reduce(
  (accumulator, currentValue) => accumulator + currentValue,
  0
); // Returns the sum: 86

reduceRight(): Reduces the array from the right to a single value using a provided function.

const concatenatedString = nums.reduceRight(
  (acc, num) => acc + num.toString(),
  ""
); // Returns the string: "6552115"

reverse(): Reverses the elements of an array in place.

const reversedArray = nums.reverse(); // Reverses nums in place: [6, 55, 2, 11, 5, 1]

shift(): Removes the first element from an array and returns that element.

const firstElement = nums.shift(); // Returns 6, and nums is now [55, 2, 11, 5, 1]

slice(): Returns a shallow copy of a portion of an array.

const slicedArray = nums.slice(1, 4); // Returns a new array: [55, 2, 11]

some(): Checks if at least one element in the array passes a certain condition.

const hasEvenNumber = nums.some((num) => num % 2 === 0); // Returns true

sort(): Sorts the elements of an array in place and returns the sorted array.

const sortedArray = nums.sort((a, b) => a - b); // Sorts nums in place: [1, 2, 5, 11, 55, 6]

splice(): Changes the contents of an array by removing or replacing existing elements and/or adding new elements.

const splicedArray = nums.splice(2, 2, 99, 100); // Removes 2 elements starting from index 2 and adds 99 and 100: [5, 11]

toString(): Returns a string representing the array and its elements.

const arrayString = nums.toString(); // Returns a string: "1,2,5,11,55,6"

unshift(): Adds one or more elements to the beginning of an array and returns the new length.

const newLength = nums.unshift(-1, 0); // Returns the new length: 8, and nums is now [-1, 0, 1, 2, 5, 11, 55, 6]

valueOf(): Returns the primitive value of the array, which is the array itself.

const primitiveValue = nums.valueOf(); // Returns nums itself

JavaScript Object Methods:

const person = {
  name: "ramu",
  age: 24,
  email: "ramubugudi4@gmail.com",
};

Object.keys(object): Returns an array of a given object's own enumerable property names, iterated in the same order that a normal loop would.

const keys = Object.keys(person); // returns [ 'name', 'age', 'email' ]

Object.values(object): Returns an array of a given object's own enumerable property values, iterated in the same order as that of the for...in loop.

const values = Object.values(person); // returns [ 'ramu', 24, 'ramubugudi4@gmail.com' ]

Object.entries(object): Returns an array of a given object's own enumerable string-keyed property [key, value] pairs, in the same order as that of a for...in loop.

const entries = Object.entries(person);
// returns [ ['name', 'ramu'], ['age', 24], ['email', 'ramubugudi4@gmail.com'] ]

Object.freeze(object): Freezes an object, preventing new properties from being added to it, existing properties from being removed, and data properties from being changed.

const frozenPerson = Object.freeze(person);
// Now, attempting to modify or add properties to frozenPerson will result in an error.

Object.assign(target, ...sources): Copies the values of all enumerable own properties from one or more source objects to a target object. It returns the modified target object.

const additionalInfo = { country: "India", occupation: "Developer" };
const extendedPerson = Object.assign({}, person, additionalInfo);
// returns { name: 'ramu', age: 24, email: 'ramubugudi4@gmail.com', country: 'India', occupation: 'Developer' }

JavaScript Map Methods:

new Map(): Creates a new Map object.

const myMap = new Map();

setMap(key, value): Sets the value for the specified key in the Map object.

myMap.set("name", "ramu");

getMap(key): Returns the value associated with the specified key in the Map object.

const value = myMap.get("name");

clearMap(): Removes all key/value pairs from the Map object.

myMap.clear();

deleteMap(key): Removes the key and its associated value from the Map object.

myMap.delete("name");

hasMap(key): Returns a boolean indicating whether the specified key is present in the Map object or not.

const hasKey = myMap.has("name");

forEachMap(callbackFn): Executes a provided function once for each key/value pair in the Map object, in insertion order.

myMap.forEach((value, key) => {
  console.log(`${key}: ${value}`);
});

entriesMap(): Returns a new Iterator object that contains an array of [key, value] for each key/value pair in the Map object.

const entries = myMap.entries();

keysMap(): Returns a new Iterator object that contains the keys for each element in the Map object in insertion order.

const mapKeys = myMap.keys();

valuesMap(): Returns a new Iterator object that contains the values for each element in the Map object in insertion order.

const mapValues = myMap.values();

size: Returns the number of key/value pairs in the Map object.

const mapSize = myMap.size;

Some of the new JavaScript methods

groupBy

Definition:

The groupBy method categorizes elements in an iterable based on the values returned by a provided callback function.

Similarities to SQL's groupBy:

Similar to SQL's groupBy, it groups elements based on a specific condition, but it operates on JavaScript iterables (arrays, maps, strings) instead of SQL tables.

Output:

Returns an object where each key represents a group and the corresponding value is an array containing all elements belonging to that group.

const person = [
  { name: "ramu", age: 24 },
  { name: "kumar", age: 27 },
  { name: "indhu", age: 30 },
  { name: "sagar", age: 10 },
  { name: "aadya", age: 7 },
];

const isMajor = ({ age }) => {
  if (age < 21) return false;
  return true;
};

const groupByResult = Object.groupBy(person, isMajor);
// {"true":[{"name":"ramu","age":24},{"name":"kumar","age":27},{"name":"indhu","age":30}],"false":[{"name":"sagar","age":10},{"name":"aadya","age":7}]}

toSpliced, toReversed, and toSorted

Definition:

These methods return a modified copy of the original input without modifying the original itself. They perform the specified operation (splice, reverse, or sort) on a copy and return the transformed result.

Mutation:

They are non-mutating methods, meaning they do not change the original input. This ensures that the original data remains intact while providing the desired transformation.

const person = [
  { name: "ramu", age: 24 },
  { name: "kumar", age: 27 },
  { name: "indhu", age: 30 },
  { name: "sagar", age: 10 },
  { name: "aadya", age: 7 },
];

const toSplicedResult = person.toSpliced(0, 1);
const toReversedResult = person.toReversed();
const toSortedResult = person.toSorted((a, b) => a.age - b.age);

// {"person":[{"name":"ramu","age":24},{"name":"kumar","age":27},{"name":"indhu","age":30},{"name":"sagar","age":10},{"name":"aadya","age":7}],"toSplicedResult":[{"name":"kumar","age":27},{"name":"indhu","age":30},{"name":"sagar","age":10},{"name":"aadya","age":7}],"toReversedResult":[{"name":"aadya","age":7},{"name":"sagar","age":10},{"name":"indhu","age":30},{"name":"kumar","age":27},{"name":"ramu","age":24}],"toSortedResult":[{"name":"aadya","age":7},{"name":"sagar","age":10},{"name":"ramu","age":24},{"name":"kumar","age":27},{"name":"indhu","age":30}]}

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