Creating and initializing arrays

Declaring, creating, and initializing an array in JavaScript is as simple, as shown by the following:

var daysOfWeek = new Array(); //{1} 
var daysOfWeek = new Array(7); //{2} 
var daysOfWeek = new Array('Sunday', 'Monday', 'Tuesday', 'Wednes day', 'Thursday', 'Friday', 'Saturday'); //{3}

We can simply declare and instantiate a new array using the keyword new (line {1}). Also, using the keyword new, we can create a new array specifying the length of the array (line {2}). A third option would be passing the array elements directly to its constructor (line {3}).

However, using the new keyword is not best practice. If you want to create an array in JavaScript, we can assign empty brackets ([]), as in the following example:

var daysOfWeek = []; 

We can also initialize the array with some elements, as follows:

var daysOfWeek = ['Sunday', 'Monday', 'Tuesday', 'Wednesday',  'Thursday', 'Friday', 'Saturday'];

If we want to know how many elements are in the array (its size), we can use the length property. The following code will give an output of 7:

console.log(daysOfWeek.length);

for (var i=0; i<daysOfWeek.length; i++){ 
  console.log(daysOfWeek[i]); 
} 

var fibonacci = []; //{1} 
fibonacci[1] = 1; //{2} 
fibonacci[2] = 1; //{3} 
 
for(var i = 3; i < 20; i++){ 
  fibonacci[i] = fibonacci[i-1] + fibonacci[i-2]; ////{4} 
} 
 
for(var i = 1; i<fibonacci.length; i++){ //{5} 
  console.log(fibonacci[i]);           //{6} 
}