How to Check If a Value Exists in an Array in JavaScript

Use the indexOf() Method

You can use the indexOf() method to check whether a given value or element exists in an array or not. The indexOf() method returns the index of the element inside the array if it is found, and returns -1 if it not found. Let's take a look at the following example:

<script>    
    var fruits = ["Apple", "Banana", "Mango", "Orange", "Papaya"];

    // Check if a value exists in the fruits array
    if(fruits.indexOf("Mango") !== -1){
        alert("Value exists!")
    } else{
        alert("Value does not exists!")
    }
</script>

ES6 has introduced the includes() method to perform this task very easily. But, this method returns only true or false instead of index number, as you can see here:

<script>    
    var fruits = ["Apple", "Banana", "Mango", "Orange", "Papaya"];
    alert(fruits.includes("Banana")); // Outputs: true
    alert(fruits.includes("Coconut")); // Outputs: false
    alert(fruits.includes("Orange")); // Outputs: true
    alert(fruits.includes("Cherry")); // Outputs: false
</script>

All modern browsers supports the includes() method and it is preferred for modern applications.