The indexOf() method returns the first index at which a given element can be found in the array, or -1 if it is not present!!

arr.indexOf(searchElement[, fromIndex = 0])

     | Parameter

-------- | ------------- Required | Arr Required | searchElement Optional | fromIndex

Return: -1 if the element is not found in the array or an integer >=0, the position of the element in the array

MDN link

Use Case: Check to see if there are any apples in the fruit basket (defined as an array)?

var basket = ['apple','orange','banana','strawberry'];

Without indexOf()

var found = false;
for(var i= 0, l = basket.length; i< l; i++){
    if(basket[i] === 'apple'){
        found = true;
                break;
    }
}
console.log(found);

With indexOf()

console.log(basket.indexOf("apple") != -1);

tags: js, array