JavaScript Array findIndex() Method
Below is the example of the Array findIndex() method to find the index of positive number from an array.
- Example:
<script>
// input array contain some elements.
var
array = [-10, -0.20, 0.30, -40, -50];
// function (return element > 0).
var
found = array.findIndex(
function
(element) {
return
element > 0;
});
// Printing desired values.
document.write(found);
</script>
- Output:
2
The arr.findIndex() method used to return the index of the first element in a given array that satisfies the provided testing function. Otherwise, -1 is returned.
- It does not execute the method once it finds an element satisfying the testing method.
- It does not change the original array.
Syntax:
array.findIndex(function(currentValue, index, arr), thisValue)
Parameters: This method accepts five parameters as mentioned above and described below:
- function: It is the function of the array that works on each element.
- currentValue: This parameter holds the current element.
- index: It is an optional parameter that holds the index of the current element.
- arr: It is an optional parameter that holds the array object the current element belongs to.
- thisValue: This parameter is optional, if a value to be passed to the function to be used as its “this” value else the value “undefined” will be passed as its “this” value.
Return value:It returns the array element index if any of the elements in the array pass the test, otherwise, it returns -1.
Below examples illustrate the Array findIndex() function in JavaScript:
- Example 1: In this example the method findIndex() finds all the indices that contain odd numbers. Since no odd numbers are present therefore it returns -1.
function isOdd(element, index, array) { return (element%2 == 1); } print([4, 6, 8, 12].findIndex(isOdd));
Output:
-1
- Example 2: In this example the method findIndex() finds all the indices that contain odd numbers. Since 7 is odd number therefore it returns its index
. function isOdd(element, index, array) { return (element%2 == 1); } print([4, 6, 7, 12].findIndex(isOdd));
Output:
2
Codes for the above function are defined as follows:
Program 1:
< script > // Input array contain elements var array = [10, 20, 30, 110, 60]; // Testing method (element > 25). function finding_index(element) { return element > 25; } // Printing the index of element which is satisfies document.write(array.findIndex(finding_index)); </ script > |
Output:
2
Program 2:
<script> // Number is prime or not prime. function isPrime(n) { if (n === 1) { return false ; } else if (n === 2) { return true ; } else { for ( var x = 2; x < n; x++) { if (n % x === 0) { return false ; } } return true ; } } // Printing -1 because prime number is not found. document.write([4, 6, 8, 12].findIndex(isPrime)); document.write( "<br />" ) // Printing 2 the index of prime number (7) found. document.write([4, 6, 7, 12].findIndex(isPrime)); </script> |
Output:
-1 2
Supported Browsers: The browsers supported by JavaScript Array findIndex() method are listed below:
- Google Chrome 45
- Microsoft Edge 12.0
- Mozilla Firefox 25.0
- Safari 7.1
- Opera 32.0