How to Check a Value Exist at Certain Array Index in JavaScript ?

Determining if a value exists at a specific index in an array is a common task in JavaScript. This article explores various methods to achieve this, providing clear examples and explanations to enhance your coding efficiency.

Below are the different ways to check if a value exists at a specific index in an array:

1. Using the typeof Operator

In JavaScript, the typeof operator returns the data type of its operand in the form of a string. The operand can be any object, function, or variable. If the value is undefined, then it doesn't exist.

Syntax:

typeof (operand);

Example: In this example, we will see the use of typeof operator for checking the value.

let arr = [1, 2, 3, 4, 5];
let value = 3;

if (typeof arr[value] !== "undefined") {
    console.log(`Value ${value} exists 
        at index ${value - 1}`);
} else {
    console.log(`Value ${value} doesn't 
        exist at index ${value - 1}`);
}

Value 3 exists 
        at index 2

2. Using the in Operator

The in operator checks if a given property or index exists in the object. For an array, you can use the in operator to check if an index exists or not.

Syntax:

prop in object

Example: In this example, we will see the use of in operator.

let arr = [1, 2, 3, 4, 5];
let n = 3;

if (n in arr) {
    console.log(`Value ${n} exists 
        at index ${arr.indexOf(n)}`);
} else {
    console.log(`Value ${n} does not 
        exist in the array`);
}

Value 3 exists 
        at index 2

3. Using the hasOwnProperty() Method

The hasOwnProperty() method is used to check if an object has a specific property or index. In the case of an array, you can use this method to check if an index exists.

Syntax:

object.hasOwnProperty( prop )

Example: In this example, we will see the use hasOwnProperty() method.

const arr = ['Geeksforgeeks', 'GFG', 'gfg'];

if (arr.hasOwnProperty(1)) {
    console.log(arr[1]);
    console.log('The index exists in the array')
} else {
    console.log('The specified index does NOT exist');
}

GFG
The index exists in the array

4. Using lodash _.includes() Method

Lodash _.includes() method is used to find whether the value is in the collection or not. If the collection is a string, it will be tested for a value sub-string, otherwise SameValueZero() method is used for equality comparisons. If the index is given and is negative, the value is tested from the end indexes of the collection as the offset.

Syntax:

_.includes( collection, value, index );

Example 1: In this example, we are checking whether the given value is present in the given collection or not by the use of the _.includes() method.

// Requiring the lodash library 
const _ = require("lodash");

// Collection of string
let name = ['gfg', 'geeks',
    'computer', 'science', 'portal'];

// Check value is found 
// or not by _.includes() method
console.log(_.includes(name, 'computer'));

// Check value is found or
// not by _.includes() method
console.log(_.includes(name, 'geeeks'));

// Check value is found or 
// not by _.includes() method
console.log(_.includes(name, 'gfg', 2));

Output:

true
false
false

5. Using the indexOf Method

In this approach we are using the indexOf method. this method searches the array for the specified value and returns the index of the first occurrence of the value if it exists in the array otherwise it returns -1 if the value is not found.

Example: In this example, we are checking whether the given value is present in the given array or not by using indexOf method.

let array = [1, 2, 3, 4, 5];
let value = 4;
let index = array.indexOf(value);
if (index !== -1) {
    console.log(`Value ${value} exists at index ${index}.`);
} else {
    console.log(`Value ${value} does not exist in the array.`);
}

Value 4 exists at index 3.

6. Using Array.prototype.at()

The Array.prototype.at() method allows you to retrieve the element at a specific index in an array. It returns undefined if the index is out of range, which simplifies the process of checking for the existence of a value at a specific index.

Example: This approach enhances code readability and maintains efficiency by leveraging a method designed explicitly for accessing array elements by index, adding value alongside the existing methods discussed in the article.

const numbers = [1, 2, 3, 4, 5];
const indexToCheck = 2; 
const valueAtIndex = numbers.at(indexToCheck);
if (valueAtIndex !== undefined) {
    console.log(`Value ${valueAtIndex} exists at index ${indexToCheck}.`);
} else {
    console.log(`No value exists at index ${indexToCheck}.`);
}

Value 3 exists at index 2.

7. Using Proxy Objects

A Proxy object in JavaScript allows you to create a handler for operations on another object or array. By defining custom behavior for various operations, you can intercept and manage accesses to properties, including checking if a value exists at a specific index.

1. Create a Proxy Handler: Define a handler object with traps for getting properties.
2. Intercept Property Access: In the handler's get trap, determine if the index exists and return a custom response.

Example:

function createArrayProxy(arr) {
    const handler = {
        get(target, prop) {
     if (Number.isInteger(Number(prop)) && Number(prop) >= 0 && Number(prop) < target.length) {
                return target[prop]; 
            }
            return undefined; 
        }
    };
    return new Proxy(arr, handler);
}
const array = [1, 2, 3, 4, 5];
const proxyArray = createArrayProxy(array);

const indexToCheck = 3;

const valueAtIndex = proxyArray[indexToCheck];

if (valueAtIndex !== undefined) {
    console.log(`Value ${valueAtIndex} exists at index ${indexToCheck}.`);
} else {
    console.log(`No value exists at index ${indexToCheck}.`);
}

Value 4 exists at index 3.