The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

1. Download Latest version or install with bower bower install array.findindex
2. Include polyfill on your web-page

<script src="dist/array-find-index-polyfill.min.js"></script>

3. Use as native method

["apple", "banana", "peach"].findIndex(function(item) {
    return item === "banana";
});
// 1

Testing in Chrome 61.0.3163 / Mac OS X 10.13.0
Native 431,077 Ops/sec
Polyfill 2,289,661 Ops/sec

See https://jsperf.com/array-prototype-find-index-polyfill

Specification on "Ecma International"
MDN examples

Code and documentation copyright 2017 Vladimir Belov. Code released under the MIT license.