Array Methods in JavaScript

Declaration and Initialization

Array Declaration

• Using array literal:

  var arr = [];
• Using Array.of() (ES6):

  var arr = Array.of(1, 2, 3);
• Using constructor:

  var arr = new Array(3); // Creates an array with 3 empty slots

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Array Properties and Methods

length

• Description: Returns or sets the number of elements in an array.
• Example:

  arr.length = 5; // Resizes the array

push()

• Description: Adds one or more elements to the end of the array.
• Example:

  arr.push(4, 5);

pop()

• Description: Removes the last element of the array.
• Example:

  arr.pop();

shift()

• Description: Removes the first element of the array.
• Example:

  arr.shift();

unshift()

• Description: Adds one or more elements to the beginning of the array.
• Example:

  arr.unshift(0);

reverse()

• Description: Reverses the order of the elements in the array.
• Example:

  arr.reverse();

concat()

• Description: Concatenates two or more arrays.
• Example:

  var newArr = arr.concat([4, 5]);

includes() (ES6)

• Description: Checks if the array includes a specific element.
• Example:

  arr.includes(2);

indexOf()

• Description: Returns the first index of the specified element, or -1 if not found.
• Example:

  arr.indexOf(2);

lastIndexOf()

• Description: Returns the last index of the specified element.
• Example:

  arr.lastIndexOf(2);

splice(position, n)

• Description: Adds or removes elements from an array at a specified position.
• Example:

  arr.splice(1, 2); // Removes 2 elements starting at index 1

slice(start, end)

• Description: Returns a shallow copy of a portion of an array without modifying the original.
• Example:

  arr.slice(1, 3);

join()

• Description: Joins all elements of an array into a string.
• Example:

  arr.join(", ");

copyWithin(from, start, end) (ES6)

• Description: Copies a sequence of elements within the array to another position.
• Example:

  arr.copyWithin(0, 2, 4);

fill(value, start, end) (ES6)

• Description: Fills all elements in an array with a static value.
• Example:

  arr.fill(0, 1, 3);

flat()

• Description: Flattens nested arrays.
• Example:

  let nestedArr = [1, [2, [3, 4]]];
  nestedArr.flat(2); // [1, 2, 3, 4]

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Static Functions

Array.from() (ES6)

• Description: Creates an array from an iterable or array-like object.
• Example:

  Array.from("hello"); // ["h", "e", "l", "l", "o"]

Array.isArray()

• Description: Checks if the provided value is an array.
• Example:

  Array.isArray(arr); // true

Array.of() (ES6)

• Description: Creates an array with the specified elements.
• Example:

  Array.of(1, 2, 3);

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Iteration Methods

entries() (ES6)

• Description: Creates an iterator object with key-value pairs.
• Example:

  let iterator = arr.entries();
  console.log(iterator.next().value); // [0, 1]

keys() (ES6)

• Description: Creates an iterator for the array keys.
• Example:

  let keys = arr.keys();
  console.log(keys.next().value); // 0

values() (ES6)

• Description: Creates an iterator for the array values.
• Example:

  let values = arr.values();
  console.log(values.next().value); // 1

every()

• Description: Checks if every element satisfies a condition.
• Example:

  arr.every((x) => x > 0);

some()

• Description: Checks if at least one element satisfies a condition.
• Example:

  arr.some((x) => x > 5);

filter()

• Description: Creates a new array with elements that satisfy a condition.
• Example:

  arr.filter((x) => x > 2);

find() (ES6)

• Description: Returns the first element that satisfies a condition.
• Example:

  arr.find((x) => x > 2);

findIndex() (ES6)

• Description: Returns the index of the first element that satisfies a condition.
• Example:

  arr.findIndex((x) => x > 2);

forEach()

• Description: Executes a provided function for each array element.
• Example:

  arr.forEach((x) => console.log(x));

map()

• Description: Creates a new array by applying a function to each element.
• Example:

  arr.map((x) => x * 2);

reduce()

• Description: Applies a function to reduce the array to a single value.
• Example:

  arr.reduce((acc, x) => acc + x, 0);

reduceRight()

• Description: Similar to reduce(), but operates from right to left.
• Example:

  arr.reduceRight((acc, x) => acc + x, 0);