test value in array javascript code example

Example 1: check if array does not contain value javascript

var fruits = ["Banana", "Orange", "Apple", "Mango"];

var n = fruits.includes("Mango"); // true

var n = fruits.includes("Django"); // false

Example 2: javascript test if it is an array

// If you want to test if a variable (object) is an instance of 
// an array. You can use the Array.isArray(varName) method
// this method takes one argument, the variable or object you want to test
// and returns true, if the argument is an array 
// or false, if the argument is not an array

if (Array.isArray(object)) {
	// is true
} else {
	// is false
}

Array.isArray([1, 2, 3, 4]); // Returns true
Array.isArray(4); // returns false
// this could be used for flattening an array of arrays

Example 3: how to Check if an array contains a string

// To check if an array contains a string 

const colors = ['red', 'green', 'blue'];
const result = colors.includes('red');

console.log(result); // true

// Or 

const colors = ['Red', 'GREEN', 'Blue'];
const result = colors.map(e => e.toLocaleLowerCase())
                     .includes('green');                          

console.log(result); // true