JavaScript program to check if an element is present in an Array or not

How to check if an element is present in an Array or not in JavaScript:

In this JavaScript example, we will learn how to check if an element is present in an Array or not in different ways. We can use a for loop or we can use the predefined array functions. Let me show you how it works with example programs.

Method 1: By using a loop:

We can use a for or while loop to iterate over an array and find if an element is present in an Array or not. The following program shows how to use a for loop to check if a number is an array:

const isInArray = (arr, n) => {
    for(let i = 0; i < arr.length; i++){
        if(arr[i] === n) return true;
    }
    return false;
}

console.log(`2 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 2)}`);
console.log(`7 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 7)}`);

In this example, the isInArray method checks if the element n is in the array arr or not. It returns one boolean value. It iterates over the array element and compares each element with n. If you run the above program, it will print:

2 is in [1, 2, 3, 4, 5, 6]: true
7 is in [1, 2, 3, 4, 5, 6]: false

• Download it on GitHub

We can also use a while loop similar to the for loop.

Method 2: With indexOf:

The indexOf method returns the first index of an element in an Array. If the element is not found in the array, it returns -1. The following program shows how to use the indexOf method to verify if an element is in an array:

const isInArray = (arr, n) => {
    return arr.indexOf(n) !== -1;
}

console.log(`2 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 2)}`);
console.log(`7 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 7)}`);

• Download it on GitHub

It will print the same output.

2 is in [1, 2, 3, 4, 5, 6]: true
7 is in [1, 2, 3, 4, 5, 6]: false

It finds the index of n in the array arr and returns false if the result of indexOf is -1. Else, it returns true.

Method 3: By using the includes method:

The includes() method checks if an element is included in an array or not and returns one boolean value. It returns true if the element is in the array. Else, it returns false.

The syntax of the includes() method is:

includes(e)
includes(e, from)

Where,

• The parameter e is the element to search in the array.
• The second parameter from is an optional parameter. This is the index to start the search. We can also use negative index for from. It will count back from the array end. It will use array-length + from if from < 0.
• If the value of from is greater than or equal to the length of the array, it will return false. If its value is smaller than -array.length, it will search the entire array.

The includes method returns a boolean value. It returns true if the element is found.

Let me modify the above example to use the includes method to check if an element is in an array or not:

const isInArray = (arr, n) => {
    return arr.includes(n);
}

console.log(`2 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 2)}`);
console.log(`7 is in [1, 2, 3, 4, 5, 6]: ${isInArray([1, 2, 3, 4, 5, 6], 7)}`);

• Download it on GitHub

It will print similar output.

How to use the includes method to start the search from a specific index:

We can use the includes method with the second parameter to search from a specific index. For example,

const isInArray = (arr, n, from) => {
    return arr.includes(n, from);
}

const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

console.log(`Search for 3 starting index 3: ${isInArray(arr, 3, 3)}`);
console.log(`Search for 3 starting index 1: ${isInArray(arr, 3, 1)}`);

• Download it on GitHub

One new parameter, from is added to the isInArray method. This parameter is passed as the second parameter to the includes method.

The first one is starting the search from index 3 and the second example is starting the search from index 1. Since the index starts at 0, the first example will print false and the second example will print true.

Search for 3 starting index 3: false
Search for 3 starting index 1: true

You might also like:

• JavaScript program to check if a number is Moran
• How to convert an image to Base64 in JavaScript
• JavaScript program to find if a number is a Magic number or not
• JavaScript replace multiple characters using single replace call
• How to find simple interest with JavaScript
• Show hide a div in JavaScript on button click