Arrays are lists of ordered, stored data. They can hold items that are of any data type.
Arrays can be created by using square brackets, with individual elements separated by commas.
// An array containing numbersconst numberArray = [0, 1, 2, 3];// An array containing different data typesconst mixedArray = [1, 'chicken', false];
Another way to creating a new instance of the
Array class and passing the elements as a comma-separated list of arguments:
const classArray = new Array(0, 1, 2, 3);
Creating an Array
The most straightforward way to create an array is using an array literal as in the above example.
const fruit = ['Apple', 'Orange', 'Banana'];
Whitespace is ignored and declarations can span multiple lines.
Arrays can also be created with the
Array class by using the
new keyword and passing in the elements as arguments:
const fruit = new Array('Apple', 'Orange', 'Banana');
Though, because the effect is exactly the same, it is preferable to use the literal method for simplicity and execution speed.
Accessing the Elements of an Array
Array elements are ordered by index values, starting at 0:
- Index 0 has the first element.
- Index 1 has the second element.
- Index 2 has the third element.
- Index n-1 has the nth element.
Individual elements in the array can be accessed using the array name and the element’s index surrounded by square brackets.
This code accesses the value of the first element in the
const fruit = ['Apple', 'Orange', 'Banana'];console.log(fruit);// Output: Apple
Array elements can be changed by accessing the element and assigning a new value to it.
const fruit = ['Apple', 'Orange', 'Banana'];fruit = 'Mango';console.log(fruit);// Output: Mango
Accessing an array using an unused index will return
undefined. However, a new value can still be assigned to an unused index of an array. When doing so, any gaps in the assigned indices will remain
const fruit = ['Apple', 'Orange', 'Banana'];fruit = 'Mango'; // a valid assignmentconsole.log(fruit);// Output: undefined
Any object can be an element of an array, including other arrays. Arrays with one or more arrays as elements are referred to as “nested arrays”. Similar to accessing the elements of a regular array, accessing elements within nested arrays requires the additional indices for referencing inner array elements.
// Create a nested arrayconst food = [['Apple', 'Orange', 'Banana'],['Strawberry', 'Blueberry', 'Raspberry'],['Potato', 'Carrot', 'Broccoli'],];// Retrieve the food string at index 2 of the array at index 1console.log(food);// Output: Raspberry// Retrieve the food string at index 1 of the array at index 0console.log(food);// Output: Orange
The same process applies to nested arrays that themselves contain nested arrays. The more “nested” the array, the more indices, or bracket pairs
[ ], are required for accessing their elements.
- Merges, or concatenates, two or more arrays.
- Creates a new array with all elements that pass the test from the provided function.
- Returns the first element in the array that satifies the given function.
- Returns the first index that passes the callback function's test. Returns -1 if no element passes the test.
- Loops over the array, passing each item in the array into the callback function provided.
- Returns the first index at which an element can be found. Returns -1 if element is not found.
- Returns true for arrays, otherwise false.
- Elements of an array are converted to strings and concatenated together, returning the resulting string.
- Returns the last index at which an element can be found. Returns -1 if element is not found.
- Returns the specific number of elements in the array.
- Creates a new array with the results of calling a function for every element in array.
- Removes the last element of an array, decrements the array length, and returns the value that it removed.
- Adds one or more elements to end of array and returns new length.
- Combines each element of an array, using a reducer function you specify, and returns a single value.
- Reverses the order of the elements of an array in place and returns the reversed array.
- Removes and returns the first element of the array. All subsequent elements will shift down one place.
- Returns a shallow copy of part of array, while original array is not modified.
- Sorts the elements of an array in place and returns the sorted array.
- Modifies array by inserting, deleting, and/or replacing array elements then returns an array of deleted elements.
- Returns a string with each of the array values, separated by commas. Does not mutate the original array.
- Adds one or more elements to beginning of array and returns new length.
- Returns the value of all the elements of the original array.