JavaScript Array findIndex | Get/Find First Occurrence Index of Array

To find the first index of an array in javascript; In this tutorial, you will learn JavaScript findIndex() method and how to search/get/find the first occurrence element index or position in an array using this javascript array method.

How to find index of an element position in an array in javaScript tutorial will take several examples for demonstration of how to find first index occurrence position in the array.

JavaScript Array findIndex() method

You can use the new method findIndex() to find first occurrence position of an array. Because in es6 enhance the capability to finding the first position of an element in the javascript array.

Syntax of the findIndex() method

The following syntax demonstration of the findIndex() method:

findIndex(callback(element[, index[, array]])[, thisArg])

Parameters

The findIndex() takes two parameters:

• The first one is the callback function and it’s optional.
• The second one is used as this inside the callback.

1) callback

The callback is a function to execute on each element of the array. It accepts 3 parameters:

• element is the current element of an array.
• index the index of the current element of an array.
• array the array that the findIndex() was called upon.

2) thisArg

The thisArg parameter is an optional object to be used this when executing the callback. If you omit the thisArg argument, the findIndex() function uses undefined.

Return value

For each element of an array, The findIndex() executes the callback function until the callback returns a truthy value.  In this case, the findIndex() immediately returns the value of that element. Otherwise, it returns undefined.

Note that, JS findIndex() method is truly different from the find() method, The find() method is used to search the first element in an array.

Examples: JavaScript findIndex()

Suppose you have a numeric array and want to search the first odd number position in it, you can use these findIndex() method for these.

See the following example:

let numbers = [1, 2, 3, 4, 5];

console.log(numbers.findIndex(e => e % 2 == 1));

Output:

0

If you want to find first even number index or position in an array, you can find the following:

let numbers = [1, 2, 3, 4, 5];

console.log(numbers.findIndex(e => e % 2 == 0));

Output:

1

Suppose that you have a list of computers objects with name and price properties as follows:

let computers = [{
    name: 'Dell',
    price: 60000
}, {
    name: 'HP',
    price: 50000
}, {
    name: 'Apple',
    price: 80000
}];

The following javascript code uses the findIndex() method to find the first computer position in an array, whose price is greater than $ 60000.

let computers = [{
    name: 'Dell',
    price: 60000
}, {
    name: 'HP',
    price: 50000
}, {
    name: 'Apple',
    price: 80000
}];
console.log(computers.findIndex(c => c.price > 60000));

Output:

2

Conclusion

In this tutorial, you have learned how to use the JavaScript Array’s findIndex() method and using this method how to find the first occurrence Index or position in an array.

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