JavaScript Array Methods

Because arrays are such a vital part of most programs, JavaScript provide many different methods and expressions for working with them. These methods and expressions can be used to manipulate arrays, search within arrays, or create whole new arrays from existing arrays.

The following methods are used sort of like utility methods, nonetheless they are very useful.

The isArray() Method

Sometimes it is necessary to know if a variable contains an array. Unfortunately, we cannot rely on the value datatype. This is because, in JavaScript, arrays are of the object datatype. So, if we were to use typeof on a array, it will return object. Fortunately, there is a method for testing if a value is an array, the isArray() method.

The isArray() method determines whether the passed value is an Array. The method will return a boolean, true if the value is an Array or false, if it is not.

// Creates an array of colors
const colors = ['blue', 'green', 'yellow', 'red', 'orange']

// Create an object of colors 
const theme = { color: 'black', background: 'white' }

// Checking the datatype of the variables
console.log(typeof colors) // object
console.log(typeof theme)  // object

// Checking the variables contain Arrays
console.log(Array.isArray(colors)) // true
console.log(Array.isArray(theme))  // false

The join() Method

The join() method creates a string by concatenating all the elements of an array. This method will become very useful when creating new HTML with JavaScript and adding it to the page.

// Creates a groceries list
const fruits = ['Apples', 'Bananas', 'Cherries']

console.log(fruits.join()) // Apples,Bananas,Cherries

console.log(fruits.join('')) // ApplesBananasCherries

console.log(fruits.join(' | ')) // Apples | Bananas | Cherries