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Array Methods Cheatsheet in JavaScript

array-methods-cheetsheet-in-javascript

Arrays are fundamental data structures in JavaScript, and having a solid understanding of array methods is essential for efficient manipulation and transformation of data.

In this blog post, we’ll present a comprehensive cheat sheet that covers all the major methods available for arrays in JavaScript.

Let’s dive into the Array Methods Cheatsheet in JavaScript.

No.MethodDescriptionExample
1.push()Adds elements to the end of an array.
Syntax: array.push(element1, element2, …);

Returns: Length of the updated array.
– Overwrites the original array.		var array = [ 1, 2, 3 ];
var returnValue = array.push( 4, 5 );
Output:
array = [ 1, 2, 3, 4, 5 ]; // Updated array.
returnValue = 5 // Length of the array.
2.pop()Removes the last element from an array.
Syntax: array.pop();

Returns: The removed element.
– Overwrites the original array.		var array = [ 1, 2, 3 ];
var returnValue = array.pop();
Output:
array = [ 1, 2 ]; // Updated array.
returnValue = 3 // Removed element.
3.unshift()Adds elements to the beginning of an array.
Syntax: array.unshift(element1, element2, …);

Returns: Length of the updated array.
– Overwrites the original array.		var array = [ 1, 2, 3 ];
var returnValue = array.unshift( 4, 5 );
Output:
array = [ 4, 5, 1, 2, 3 ]; // Updated array.
returnValue = 5 // Length of the array.
4.shift()Removes the first element from an array.
Syntax: array.shift();

Returns: The removed element.
– Overwrites the original array.		var array = [ 1, 2, 3 ];
var returnValue = array.shift();
Output:
array = [ 2, 3 ]; // Updated array.
returnValue = 1 // Removed element.
5.concat()Returns the first element in the array that satisfies a provided testing function.
Syntax: array.find(function(currentValue, index, arr),thisValue);

Returns: The value of the first element that passes the test.
Otherwise, it returns undefined.		var array1 = [ 1, 2 ];
var array2 = [ 3, 4 ];
var newArray = array1.concat(array2);
Output: newArray = [ 1, 2, 3, 4 ];
6.slice()Extracts a section of an array.
Syntax: array.slice(start_position, end_position)
– start_position = default is 0.
– end_position = default is the last element.

Returns: New array with extracted elements.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var newArray = array.slice( 1, 3 );
Output:
newArray = [ 2, 3 ];
array = [ 1, 2, 3, 4, 5 ]; // original array.

var array = [ 1, 2, 3, 4, 5 ];
var newArray = array.slice( 1 );
Output:
newArray = [ 2, 3, 4, 5 ];
array = [ 1, 2, 3, 4, 5 ];; // original array.
7.splice()Joins all elements of an array into a string with provided separator.
Syntax: array.join(separator);

Returns: Joined elements as a string.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var newArray = array.splice( 2, 1, ‘a’, ‘b’ );
Output:
newArray = [ 3 ];
array = [ 1, 2, ‘a’, ‘b’, 4, 5 ];
8.join()Returns the first element in the array that satisfies a provided testing function.
Syntax: array.find(function(currentValue, index, arr),thisValue);

Returns: The value of the first element that passes the test.
Otherwise it returns undefined.		var array = [ 1, 2, 3 ];
var joinedString = array.join( ‘-‘ );
Output: joinedString = “1-2-3”
9.indexOf()Returns the first index at which a given element is found in the array.
Syntax: array.indexOf(item, start_position_for_search)
start_position_for_search = default 0;

Returns: index of search element.
Returns -1 if the value is not found.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var index = array.indexOf( 3 );
Output: index = 2 // Index of 3

var index = array.indexOf( 3, 3 );
Output: index = -1 // Index of 3 searched from index 3 hence not found.
10.lastIndexOf()Returns the last index at which a given element is found in the array.
Syntax: array.lastIndexOf(item, start_position_for_search)
– start_position_for_search = Default is the last element.

Returns: Last index of search element.
Returns -1 if the index is not found.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5, 3 ];
(indexes –> 0, 1, 2, 3, 4, 5)
var lastIndex = array.lastIndexOf( 3 );
Output: lastIndex = 5 // Last index of 3
11.includes()Checks if an array includes a certain element.
Syntax: array.includes(element, start_position_for_search);
– start_position_for_search = default as 0.

Returns: True if the value is found, otherwise false.
– Does not change the original array.		var array = [ 1, 2, 3 ];
var includesThree = array.includes( 3 );
Output: includesThree = true;
12.forEach()Executes a provided function once for each array element.
Syntax: array.forEach(function(currentValue, index, arr), thisValue);

Returns: undefined.
– Does not change the original array.		var array = [ 1, 2, 3 ];
array.forEach(element => console.log(element));
Output: 1, 2, 3
13.map()Creates a new array with the results of calling a provided function on every element in the array.
Syntax: array.map(function(currentValue, index, arr), thisValue);

Returns: new array with updated results.
– Does not change the original array.
var array = [ 1, 2, 3 ];
var newArray = array.map(element => element * 2);
Output: newArray = [ 2, 4, 6 ];
14.filter()Creates a new array with all elements that pass a test implemented by the provided function.
Syntax: array.filter(function(currentValue, index, arr), thisValue);

Returns: Array of elements that pass the test. Empty array if no elements pass the test.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var filteredArray = array.filter(element => element % 2 === 0);
Output: filteredArray = [ 2, 4 ];

var filteredArray = array.filter(element => element % 6 === 0);
Output: filteredArray = [ ];
15.reduce()Applies a function to reduce the array to a single value.
Syntax: array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

– total = initialValue, or the previously returned value of the function.
– currentValue = optional.
– currentIndex = optional.
– arr = optional.

Returns: The accumulated result.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var sum = array.reduce((acc, curr) => acc + curr, 0);
Output: sum = 15
16.reduceRight()Similar to reduce(), but processes the array from right to left.

Returns: The accumulated result.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var result = array.reduceRight((acc, curr) => acc – curr);
Output: result = -13
17.find()Returns the index of the first element in the array that satisfies a provided testing function.
Syntax: array.findIndex(function(currentValue, index, arr), thisValue)

Returns: The value of the first element that passes the test.
Otherwise it returns undefined.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var foundElement = array.find(element => element > 3);
Output: foundElement = 4
18.findIndex()Checks if at least one element in the array satisfies a provided testing function.
Syntax: array.some(function(value, index, arr), this);

Returns: true if any of the array elements pass the test, otherwise false.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var foundIndex = array.findIndex(element => element > 3);
Output: foundIndex = 3 // Index of 4
19.some()Checks if at least one element in the array satisfies a provided testing function.
Syntax: array.some(function(value, index, arr), this);

Returns: true if any of the array elements pass the test, otherwise false.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var hasEvenNumber = array.some(element => element % 2 === 0);
Output: hasEvenNumber = true
20.every()Checks if all elements in the array satisfy a provided testing function.
Syntax: array.every(function(currentValue, index, arr), thisValue);

Returns: true if all elements pass the test, otherwise false.
– Does not change the original array.		var array = [ 1, 2, 3, 4, 5 ];
var allPositive = array.every(element => element > 0);
Output: allPositive = true
21.sort()Sorts the elements of an array in place.
Syntax: array.sort(compareFunction);

Returns: The array with the items sorted.
– Overwrites the original array.
– Does not change the original array.		var array = [ 3, 1, 4, 2, 5 ];
var sortedArray = array.sort();
Output:
sortedArray = [1, 2, 3, 4, 5] // returned array.
array = [1, 2, 3, 4, 5] // Original array.
22.reverse()Reverses the order of the elements in an array.
Syntax: array.reverse();

Returns: The reversed array.
– Overwrites the original array.		var array = [ 1, 2, 3, 4, 5 ];
var reversedArray = array.reverse();
Output:
reversedArray = [ 5, 4, 3, 2, 1 ] // returned array.
array = [ 5, 4, 3, 2, 1 ] // original array.
23.isArray()Checks if a value is an array.
Syntax: Array.isArray(obj);

Returns: true if the object is an array, otherwise false.
– Does not change the original array.		var array = [ 1, 2, 3 ];
var isArrayTrue = Array.isArray(array);

Output: isArrayTrue = true
24.lengthProperty that represents the number of elements in an array.
Syntax: array.length;

Returns: The number of elements in the array.
– Does not change the original array.		var array = [ 1, 2, 3 ];
var length = array.length;

Output: length = 3 // length of the array.

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