Find index of element in array JavaScript

In this post, you will learn how to find the index of element in an array using JavaScript. There are several ways to find the index of element in array. Here, we have mentioned most of them-

JavaScript find index of element in an array using indexOf() method

The indexOf() method returns the position of the first occurrence of an element. It returns -1 if the value is not found.

array.indexOf(item, start)

Here, item is the element that you want to find within an array, and start is the position where to start the search.

const fruits = ["Bus", "Truck", "Car", "Bike", "Scooty"];
let index = fruits.indexOf("Car",0);
console.log("Index of Car: "+ index);

Index of Car: 2

const fruits = ["Bus", "Truck", "Car", "Bike", "Scooty"];
let index = fruits.indexOf("Car",-2);
console.log("Index of car: "+ index);

Index of car: -1

JavaScript find index of element in an array using findIndex() method

The findIndex() method of JavaScript returns the index of the element that satisfies a testing function or -1 if no element passed the test.

array.findIndex(function(currentValue, index, arr), thisValue)

Here, function is the function to execute on each element in the array until the function returns true, it takes three arguments element, index, and array and the thisValue is an optional object to be used when executing the callback.

In the given example, the findIndex() method finds the element index that contains an odd number.

const arr = [44, 64, 22, 89, 56, 34];

function isOdd(element, index, array) {
      return (element%2 == 1);
}
      
console.log((arr.findIndex(isOdd))); 

In the given example, the findIndex() method finds the element index that contains positive number.

const arr = [-44, -64, -22, 89, -56, -34];

var getPositive = arr.findIndex(function (element) {
  return element > 0;
});
      
console.log("Index with Positive number: "+getPositive); 

Index with Positive number: 3

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