JavaScript Array Cheat Sheet
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Hey there everyone, In this detailed blog, you will see and learn all the basic array methods and operations in JavaScript.
Basic Methods
1.concat
[1,2,3].concat([4,5])
Return Type : Array
Description : Concatenate the array passed to concat to the end of the array
Add the elements 4 and 5 to the end of the
array
result : [1,2,3,4,5]
2.slice
[1,2,3,4].slice(1, 3)
Return Type : Array
Description : Copy part of an array starting at the index of the first parameter and stopping at the index of the second parameter, but not including the last index
Copy the values in index 1 and 2 into a new
array
result : [2,3]
3.reverse
[1,2,3].reverse()
Return Type : Array(Modifies The Array)
Description : Reverse the order of the elements in an array
Reverse the order of the elements
in an array
result : [3,2,1]
4.join
[1,2,3].join(“, “)
Return Type : String
Description : Combine each element of the array into a string with the value passed to join placed between each value
Add a comma and a space between each
element in the array
result : 1, 2, 3
Array Manipulation
1.push
[1,2,3].push(4, 5)
Return Type : Number(Modifies The Array Return length of array)
Description : Add one or more elements to the end of the array
Add 4 and 5 to the end of the array
result : [1 ,2 ,3 ,4 ,5]
2.pop
[1,2,3].pop()
Return Type : Element(Modifies The Array Return removed element)
Description : Remove the last element from the array
Remove the value 3 from the array
result : [1 ,2]
3.shift
[1,2,3].shift()
Return Type : Element(Modifies The Array Return removed element)
Description : Remove the first element from the array
Remove the value 1 from the array
result : [2,3]
4.unshift
[1,2,3].unshift(4, 5)
Return Type : Number(Modifies The Array Return length of array)
Description : Add one or more elements to the start of the array
Add 4 and 5 to the start of the array
result : [4,5,1,2,3]
5.splice
[1,2,3].splice(1, 1, 4, 5)
Return Type : Number(Modifies The Array Return length of array)
Description : Starting at the index specified by the first parameter, remove the number of elements specified by the second parameter and then add elements to the array for all remaining parameters at the index specified by the first parameter
Starting at index 1, remove 1 element and then
add the elements 4 and 5 at index 1.
result : [1,4,5,3]
Higher Order Functions
1.forEach
[1,2,3].forEach(n => console.log(n))
Return Type : Undefined
Description : Execute the function passed to forEach for each element in the array similar to a for loop
Log out each element in the array
result : None
2.map
[1,2,3].map(n => n * 2)
Return Type : Array
Description : Return a new array which contains the return result of running each item through the function passed to map
Create a new array with all values doubled
result : [2,4,6]
3.filter
[1,2,3].filter(n => n > 2)
Return Type : Array
Description : Return a new array which only contains values that return true to the function passed to filter
Create a new array with only values greater
than 2
result : [3]
4.find
[1,2,3].find(n => n > 2)
Return Type : Element
Description : Select the first element that returns true to the function passed to find
Get the first element greater than 1
result : 2
5.findIndex
[1,2,3].findIndex(n => n > 1)
Return Type : Number
Description : Get the index of the first element that returns true to the function passed to find
Get the index of the first element greater than 1
result : 1
6.every
[1,2,3].every(n => n > 1)
Return Type : Boolean
Description : Return true if every element in the array returns true from the function passed to every
Check if every element is greater than 1
result : false
7.some
[1,2,3].some(n => n > 1)
Return Type : Boolean
Description : Return true if at least one element in the array returns true from the function passed to some
Check if any element is greater than 1
result : true
8.reduce
[1,2,3].reduce((sum, n) => sum + n, 0)
Return Type :Any Value
Description : Reduce the array to one single value by starting the sum at the second value passed to reduce and updating the sum with the return value of each iteration
Sum all the numbers in the array starting with 0
result : 6
Basic Value Check
1.indexOf
[1,2,1].indexOf(1)
Return Type :Number
Description : Return the first index of the value passed to indexOf or return -1 if the value cannot be found
Get the first index of 1 in the array
result : 0
2.lastIndexOf
[1,2,1].lastIndexOf(1)
Return Type :Number
Description : Return the last index of the value passed to indexOf or return -1 if the value cannot be found
Get the last index of 1 in the array
result : 2
3.includes
[1,2,3].includes(4)
Return Type :Boolean
Description : Return true if the value passed to includes is in the array
Check if the value 4 is in the array
result : false
4.length
[1,2,3].length
Return Type :Number
Description : Return the length of the array
result : 3
