Arrays are used to store multiple values in a single variable.
Each value is called an element, and each element has a numeric position in the array, known as its index.
Arrays are zero-indexed, meaning the first element is at index 0, the second at index 1, and so on.
Arrays can contain any data type, including numbers, strings, and objects.
const arr1 = [2, 4, 6]; array
arr1[0]; element at index 0 → 2
arr1[1]; element at index 1 → 4
arr1[2]; element at index 2 → 6
arr1[3]; element at index 3 → undefined index not found
Numbers are used to represent both integer and floating-point values.
Numbers are most commonly expressed in literal forms like 255 or 3.14159 ↴
let num1 = 5; → number
let num2 = 2.5; → number
let num3 = num1 + num2;
console.log(num3); returns ↴
7.5 → number
Find maximum number in an array using the in-built sort method.
sort() method sorts the elements of an array as strings.
By default, the elements of the array are converted to strings and sorted in ascending order by comparing their sequences based on their UTF-16 code unit values.
sort() method returns a reference to the original array, so mutating the returned array will mutate the original array as well.
sort() method is stable, it preserves the order of items in an array when their values are the same.
sort() method can sort an array of numbers, strings, or objects with custom functions.
syntax
array.sort()
By default the sort() method sorts the array in ascending order with the elements converted to strings.
This can lead to unexpected results when sorting arrays of numbers.
const arr2 = [2, 11, 1, 22, 33, 3];
arr2.sort(); returns ↴
[1, 11, 2, 22, 3, 33] NOT sorted accurately
To solve this limitation, a comparison callback function can be used to define the desired sorting order.
callback function a function passed into another function as an argument, which is then invoked within the outer function.
When sorting numbers,
For sorting an array of numbers in ascending order, the comparison function should subtract the second number from the first number.
syntax
array.sort(compareFunction)
comparison function
(a, b) => a - b compares two elements ↴
a and b
a - b calculates the difference between the two numeric values ↴
If the result is ...
negative → a sorted before b
positive → a sorted after b
zero → order remains unchanged.
const arr3 = [2, 11, 1, 22, 33, 3];
arr3.sort((a, b) => a - b); returns ↴
[1, 2, 3, 11, 22, 33] → ascending order
The comparison function can be changed to sort in descending order by swapping the elements for comparison to b - a
const arr4 = [2, 11, 1, 22, 33, 3];
arr4.sort((a, b) => b - a); returns ↴
[33, 22, 11, 3, 2, 1] → descending order
Initialize an array from which to find the maximum number.
const array1 = [5, 4, 6, 8, 7]; → user input
Define a function findMaxNumber to find maximum number.
function findMaxNumber(arr) {}
The function takes an array as input arr and returns the largest number found in that array. The original array is updated.
sort() method mutates the original array.
Sort the array in descending order (a, b) => b - a
const sortedArr = arr.sort((a, b) => b - a) sortedArr
Return the first element of the sorted array, which is the maximum number.
return sortedArr[0]
Call the function with ↴
findMaxNumber(array1);
Find the maximum number in an array.
const array1 = [5, 4, 6, 8, 7];
function findMaxNumber(arr) {
const sortedArr = arr.sort((a, b) => b - a);
return sortedArr[0];
}
call function
findMaxNumber(array1); returns ↴
8
Alternative - sort array in ascending order and find last element in array.
const sortedArr = arr.sort((a, b) => a - b);
return sortedArr[arr.length - 1];
Alternative using built-in Math.max() method.
const arr = [5, 4, 6, 8, 7]; numbers only
Math.max(...arr); returns ↴
8
Alternative using slice() method to prevent mutating original array ↴
arr.sort((a, b) => b - a); ↴
arr.slice().sort((a, b) => b - a);
Alternative using toSorted() method to prevent mutating original array ↴
arr.sort((a, b) => b - a); ↴
arr.toSorted((a, b) => b - a);