05 - Basic Array Methods

Properties that contain functions are called methods of the value they belong to. For example, .toUpperCase() is a method of a string.

arr.at(pos)

The at() method returns an indexed element from an array. It is similar to using [], but [] does not support accessing the last index using [-1]. This is because [] is used for both arrays and objects, and obj[-1] refers to the key -1, not the last property of the object. The at() method was introduced to solve this issue.

const fruits = ["Banana", "Orange", "Mango"];

let fruit = fruits.at(2);  // Mango
let fruit = fruits[2];     // Mango

alert(fruits[-1]);         // Error
alert(fruits.at(-1));      // Mango

str.split(delim)

The split() method splits a string into an array using the specified delimiter delim. F

To split a comma-delimited string:

let names = `John, Pete, Mary`;

let arr = names.split(', ');

for (let name of arr) {
	alert(`A message to ${name}.`);
}

The split() method has an optional second argument: a numeric value that limits the length of the resulting array. If provided, extra elements are ignored.

Split into letters:

let str = 'test';
alert(str.split(''));  
// ["t", "e", "s", "t"]

arr.reverse()

The reverse() method reverses the order of elements in an array and returns the modified array.

let arr = [1, 2, 3, 4, 5];
arr.reverse();

alert(arr);  
// [5, 4, 3, 2, 1]

Array to String Conversion

If you need to save the contents of an array in textual form for later reuse, it’s better to serialize the array using JSON.stringify() rather than using other methods like join() or toString().

arr.join(glue)

The join() method is the reverse of split(). It converts an array into a string, concatenating the elements with the specified separator glue.

const arr = ["Banana", "Orange", "Mango"];

let str = arr.join(" * ");  // "Banana * Orange * Mango"
let str = arr.join(';');    // "Banana;Orange;Mango"
alert(str);                 // "Banana;Orange;Mango"

let a = [1, 2, 3];
alert(a.join());    // "1,2,3"
alert(a.join(" ")); // "1 2 3"
alert(a.join(""));  // "123"

let b = new Array(10);
alert(b.join("-")); // "--------" (a string of 9 hyphens)

toString()

The toString() method is available to all JavaScript objects, including arrays. It converts an array into a string of comma-separated values. This is the default behavior when an array is output.

const fruits = ["Banana", "Orange", "Mango"];

alert(fruits.toString());  // "Banana,Orange,Mango"
alert(fruits);             // "Banana,Orange,Mango" (same as above)

For an array, this works like join with no arguments

[1, 2, 3].toString();       // "1,2,3"
["a", "b", "c"].toString(); // "a,b,c"
[1, [2, "c"]].toString();   // "1,2,c"