What is an Array?
- An array is a special variable, which can hold more than one value.
Advantages of array.
Arrays store multiple data of similar types with the same name. As the array is of fixed size and stored in contiguous memory locations there is no memory shortage or overflow. It is helpful to store any type of data with a fixed size.
It can be defined as a sequence of objects which are of the same data type. It is used to store a collection of data, and it is more useful to think of an array as a collection of variables of the same type.
What do you call the things inside an array?
- Each variable or object in an array is called an element.
How to write an array?
we can write array use square brackit like this a = [1, 2, 3, "abc" , "cd" ]
// It can be any value we can store in array
const array = ['Apple', 'Banana', 'Strawberry' , true, false, 10, 20];
// also we can do for array
const store =new Array('Apple', 'Banana', 'Strawberry' , true, false, 10, 20)
// The two examples above do exactly the same.
// There is no need to use new Array().
How to count an array?
- We count from 0. like ...
- Accessing Array Elements.
- You access an array element by referring to the index number:
const cars = ["Jon Deo", "Hitesh Sir", "jsdeveloper"];
let car = cars[0];
// Note: Array indexes start with 0.
//[0] is the first element. [1] is the second element.
2 . Array at()
- The at() method takes an integer value and returns the item at that index, allowing for positive and negative integers. Negative integers count back from the last item in the array
const array1 = [5, 12, 8, 130, 44];
let index = 2;
console.log(`Using an index of ${index} the item returned is ${array1.at(index)}`);
// expected output: "Using an index of 2 the item returned is 8"
3 . Array concat().
The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.
const array1 = ['a', 'b', 'c'];
const array2 = ['d', 'e', 'f'];
const array3 = array1.concat(array2);
console.log(array3);
// expected output: Array ["a", "b", "c", "d", "e", "f"]
4 . Array .copyWithin()
- The copyWithin() method shallow copies part of an array to another location in the same array and returns it
without modifying its length.
const array1 = ['a', 'b', 'c', 'd', 'e'];
// copy to index 0 the element at index 3
console.log(array1.copyWithin(0, 3, 4));
// expected output: Array ["d", "b", "c", "d", "e"]
// copy to index 1 all elements from index 3 to the end
console.log(array1.copyWithin(1, 3));
// expected output: Array ["d", "d", "e", "d", "e"]
5 . Array entries()
- The entries() method returns a new Array Iterator object that contains the key/value pairs for each index in the array.
const array1 = ['a', 'b', 'c'];
const iterator1 = array1.entries();
console.log(iterator1.next().value);
// expected output: Array [0, "a"]
console.log(iterator1.next().value);
// expected output: Array [1, "b"]
6 . Array every()
- The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value.
const isBelowOrNot = (currentValue) => currentValue < 40;
const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every(isBelowThreshold));
// expected output: true
7 . Array fill()
- The fill() method changes all elements in an array to a static value, from a start index (default 0) to an end index (default array.length).
It returns the modified array.
const array1 = [1, 2, 3, 4];
// fill with 0 from position 2 until position 4
console.log(array1.fill(0, 2, 4));
// expected output: [1, 2, 0, 0]
// fill with 5 from position 1
console.log(array1.fill(5, 1));
// expected output: [1, 5, 5, 5]
console.log(array1.fill(6));
// expected output: [6, 6, 6, 6]
8 . Array values()
- The values() method
returns a new arrayiterator object that contains the values for each index in the array.
const array1 = ['a', 'b', 'c'];
const iterator = array1.values();
for (const value of iterator) {
console.log(value);
}
// expected output: "a"
// expected output: "b"
// expected output: "c"
9 . Array unshift()
- The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.
const array1 = [1, 2, 3];
console.log(array1.unshift(4, 5));
// expected output: 5
console.log(array1);
// expected output: Array [4, 5, 1, 2, 3]
// eg.
unshift(element0)
unshift(element0, element1)
unshift(element0, element1, /* … ,*/ elementN)
10 . Array toString().
- The toString() method returns a string representing the specified array and its elements.
const array1 = [1, 2, 'iNeuron', 'lco'];
console.log(array1.toString());
// expected output: "1,2,iNeuron,lco"
11 . Array splice()
- The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place. To access part of an array without modifying it, see slice().
const months = ['Jan', 'March', 'April', 'June'];
months.splice(1, 0, 'Feb');
// inserts at index 1
console.log(months);
// expected output: Array ["Jan", "Feb", "March", "April", "June"]
months.splice(4, 1, 'May');
// replaces 1 element at index 4
console.log(months);
// expected output: Array ["Jan", "Feb", "March", "April", "May"]
splice(start)
splice(start, deleteCount)
splice(start, deleteCount, item1)
splice(start, deleteCount, item1, item2, itemN)
12 . Array sort().
- The sort() method sorts the elements of an array in place and returns the reference to the same array, now sorted. The default sort order is ascending.
const months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months);
// expected output: Array ["Dec", "Feb", "Jan", "March"]
const array1 = [1, 30, 4, 21, 100000];
array1.sort();
console.log(array1);
// expected output: Array [1, 100000, 21, 30, 4]
13 . Array some()
- The some() method tests whether at least one element in the array passes the test implemented by the provided function. It returns true if, in the array, it finds an element for which the provided function returns true; otherwise it returns false. It doesn't modify the array.
const array = [1, 2, 3, 4, 5];
// checks whether an element is even
const even = (element) => element % 2 === 0;
console.log(array.some(even));
// expected output: true
14 . Array slice()
- The slice() method returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included) where start and end represent the index of items in that array. The original array will not be modified.
const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];
console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]
console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]
console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]
console.log(animals.slice(-2));
// expected output: Array ["duck", "elephant"]
console.log(animals.slice(2, -1));
// expected output: Array ["camel", "duck"]
console.log(animals.slice());
// expected output: Array ["ant", "bison", "camel", "duck", "elephant"]
15 . Array shift()
- The shift() method removes the first element from an array and returns that removed element. This method changes the length of the array.
const array1 = [1, 2, 3];
const firstElement = array1.shift();
console.log(array1);
// expected output: Array [2, 3]
console.log(firstElement
16 . Array pop()
- The pop() method removes the last element from an array and returns that element. This method changes the length of the array.
const plants = ['broccoli', 'cauliflower', 'cabbage', 'kale', 'tomato'];
console.log(plants.pop());
// expected output: "tomato"
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage", "kale"]
plants.pop();
console.log(plants);
// expected output: Array ["broccoli", "cauliflower", "cabbage"]
17 . Array push()
- The push() method adds one or more elements to the
endof an array and returns the new length of the array.
const animals = ['pigs', 'goats', 'sheep'];
const count = animals.push('cows');
console.log(count);
// expected output: 4
console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows"]
animals.push('chickens', 'cats', 'dogs');
console.log(animals);
// expected output: Array ["pigs", "goats", "sheep", "cows", "chickens", "cats", "dogs"]
18 . Array Join()
- The Array.of() method creates a new Array instance from a variable number of arguments, regardless of number or type of the arguments.
Array.of(7); // [7]
Array(7); // array of 7 empty slots
Array.of(1, 2, 3); // [1, 2, 3]
Array(1, 2, 3); // [1, 2, 3]
Array.of(element0)
Array.of(element0, element1)
Array.of(element0, element1, /* … ,*/ elementN)
19 . Array find()
- The find() method returns the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned.
const array1 = [5, 12, 8, 130, 44];
const found = array1.find(element => element > 10);
console.log(found);
// expected output: 12
20 . Array findIndex()
- The findIndex() method returns the index of the first element in an array that satisfies the provided testing function. If no elements satisfy the testing function, -1 is returned.
const array1 = [5, 12, 8, 130, 44];
const isLargeNumber = (element) => element > 13;
console.log(array1.findIndex(is
// Arrow function
findIndex((element) => { /* … */ } )
findIndex((element, index) => { /* … */ } )
findIndex((element, index, array) => { /* … */ } )
// Callback function
findIndex(callbackFn)
findIndex(callbackFn, thisArg)
// Inline callback function
findIndex(function(element) { /* … */ })
findIndex(function(element, index) { /* … */ })
findIndex(function(element, index, array){ /* … */ })
findIndex(function(element, index, array) { /* … */ }, thisArg)
21 . Array flat()
- The flat() method creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.
const arr1 = [0, 1, 2, [3, 4]];
console.log(arr1.flat());
// expected output: [0, 1, 2, 3, 4]
const arr2 = [0, 1, 2, [[[3, 4]]]];
console.log(arr2.flat(2));
// expected output: [0, 1, 2, [3, 4]]
flat()
flat(depth)
// The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.