In JavaScript, we can check if an array includes an element in multiple ways. One of the easiest and efficient ways is by using the includes() method.
The includes() method determines whether an array includes a certain element, returning either true or false as appropriate. This method compares the element with every item in the array using strict equality (the same method used by the === operator).
Here is an example of using the includes() method:
const numbers = [10, 20, 30, 40, 50];
console.log(numbers.includes(30)); // Output: true
console.log(numbers.includes(25)); // Output: false
In this example, we first create an array called numbers that contains multiple elements. We then use the includes() method to check if the number 30 is present within the array. As 30 is included in the array, the output is true. We then check if another number, 25, is present within the array, which is not included in the array, so the output is false.
It's important to note that the includes() method is case-sensitive, which means that it will match elements based on their exact value and case. So, for example, includes('apple') will not match with 'Apple'.
Another way to check if an element exists in an array is by using the indexOf() method. This method returns the index of the element if it exists in the array, and -1 if it does not exist. Here is an example:
const fruits = ['apple', 'banana', 'grape', 'kiwi'];
console.log(fruits.indexOf('banana')); // Output: 1
console.log(fruits.indexOf('orange')); // Output: -1
In this example, we first create an array called fruits, which contains multiple elements. We then use the indexOf() method to check if the string 'banana' exists in the fruits array. Since it exists in the array, the output is 1, which is the index at which the element is found. We then check if another string, 'orange', exists in the fruits array, but it does not exist, so the output is -1.
Both includes() and indexOf() methods are very handy in checking if an element exists in an array in JavaScript- ECMAScript 2021.