Node.js Tutorial - Node.js Arrays

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To create arrays, you can either use traditional notation or array literal syntax :

var arr1 = new Array();
var arr2 = [];

As with objects, the literal syntax version is preferred.

We can test if an object is an array using the Array.isArray function:

var arr2 = [];
Array.isArray(arr2);
Array.isArray({});

We can create arrays quite easily in JavaScript using [].

Arrays have many useful functions.

var myData = []; 
// w  ww. j a va  2  s.  c  o  m
myData.push(1); // add at the end 
console.log(myData); // prints [1] 

myData.unshift(2); // add to the top 
console.log(myData); // prints [2,1] 

// Arrays are zero index based: 
console.log(myData[0]); // prints 2 

The code above generates the following result.

Example

The array type in JavaScript length property returns the element count.

var arr2 = [];
arr2.length;
console.log(arr2);
var arr3 = [ 'cat', 'rat', 'bat' ];
console.log(arr3.length);

The code above generates the following result.

By default, arrays in JavaScript are numerically indexed:

var arr3 = [ 'cat', 'rat', 'bat' ];
for (var i = 0; i < arr3.length; i++) {
    console.log(arr3[i]);
}

The code above generates the following result.

To add an item to the end of an array, you can do one of two things:

var arr3 = [ 'cat', 'rat', 'bat' ];
arr3.push("mat");
console.log(arr3);
arr3[arr3.length] = "fat";
console.log(arr3);

The code above generates the following result.

We can specify the index of the element where you want to insert a new element.

If this element is past the last element, the elements in between are created and initialized with the value undefined :

var arr3 = [ 'cat', 'rat', 'bat' ];
arr3[20] = "splat";
console.log(arr3);

The code above generates the following result.

Note

To delete an item from an array, use the splice function, which takes an index and the number of items to delete.

What it returns is an array with the extracted items, and the original array is modified such that they no longer exist there:

var arr3 = [ 'cat', 'rat', 'bat', 'cat', 'rat', 'bat' ];
arr3.splice(2, 2);
console.log(arr3);
console.log(arr3.length);

The code above generates the following result.

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