An array is the collection of ordered items. These ordering collections make array index zero-based.
Creating and Accessing an Array
Creating an Array
Arrays are created as an object. See the syntax below:
array = new Array(item1, item2, ...,itemN);
The above syntax can be rewritten as shown below:
array = [ item1, item2, ...,itemN ];
The items, item1, item2, ...,itemN
are of any data type.
See the example below:
// const arr = new Array(true, "Bob", 34, 7n);
const arr = [ true, "Bob", 34, 7n ];
Alternatively, you can append elements to an element.
const arr = [];
arr[0] = true;
arr[1] = "Bob";
arr[2] = 34,
arr[3] = 7n
console.log(arr); // [ true, "Bob", 34, 7n ]
Accessing an Array
Arrays items are in order or numbered starting from zero (0, 1, ..., N
).
See the example below:
const arr = [ true, "Bob", 34, 7n ];
console.log( arr[0] ) // true
console.log( arr[1] ) // Bob
console.log( arr[2] ) // 34
console.log( arr[3] ) // 7n
The length
number property determines the number of items in an array.
See the example below:
const arr = [ true, "Bob", 34, 7n ];
arr.length; // 4
The example above shows the array's last item index is arr.length - 1
.
See the example below:
const arr = [ true, "Bob", 34, 7n ];
arr[arr.length - 1]; // 7n
Trailing comma
An array, just like an object, may end with a comma:
const arr = [
'Melon',
{ name: 'Bello' },
true,
function() {
console.log('Hello World!');
}
];
console.log( arr[1].name ); // Bello
arr[3](); // Hello World!
Array is an object and thus behaves like an object.
typeof arr; // object
Array queue
In computer science, ordered collection of elements supports two operations:
push
shift
push
The push
method appends an item to an array.
See the example below:
const fruits = [ "Apple", "Orange" ];
fruits.push("Melon");
console.log( fruits ); // [ 'Apple', 'Orange', 'Melon' ]
The above example can be rewritten as shown below:
const fruits = [ "Apple", "Orange" ];
fruits[fruits.length] = "Melon";
console.log( fruits ); // [ 'Apple', 'Orange', 'Melon' ]
shift
Opposite to the push
method, an item can be removed (and returned) at the beginning of an array.
const fruits = [ "Apple", "Orange", "Melon" ];
console.log( fruits.shift() ); // Apple => returned removed item
console.log( fruits ); // [ 'Orange', 'Melon' ]
Array stack
In computer science, ordered collection of elements supports two operations:
push
pop
pop
The pop
method removes the last element of the array and returns it:
const fruits = [ "Apple", "Orange", "Melon" ];
console.log( fruits.pop() ); // Melon => returned removed item
console.log( fruits ); // [ 'Apple', 'Orange' ]
The shift
method removes an element from the beginning of an array; while the pop
method removes an element from the end of an array.
See the example below:
const fruits = [ "Apple", "Orange", "Melon" ];
fruits.shift();
console.log(fruits); // [ "Orange", "Melon" ]
The example above is the same as below:
const fruits = [ "Apple", "Orange", "Melon" ];
fruits[0] = fruits[1]; // [ 'Orange', 'Orange', 'Melon' ]
fruits[1] = fruits[fruits.length-1]; // [ 'Orange', 'Melon', 'Melon' ]
fruits[fruits.length-1] = fruits[fruits.length];
// [ 'Orange', 'Melon', undefined ]
console.log( fruits.pop() ); // undefined
console.log(fruits); // [ "Orange", "Melon" ]
Methods
push/pop
run fast, whileshift/unshift
are slow.For stacks the principle is based on LIFO (Last-In-First-Out) while queues, FIFO (First-In-First-Out) principle. In computer science, the data structure that allows this is called deque.
unshift
The unshift
method is the opposite of push
, it adds an element to the beginning of an array.
const fruits = [ "Orange", "Melon" ];
fruits.unshift("Apple");
console.log(fruits) // [ Apple, "Orange", "Melon" ]
Happy coding
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