ES2015 `Array#findIndex()` ponyfill
npm install array-find-index> ES2015 Array#findIndex() ponyfill
```
$ npm install --save array-find-index
`js
const arrayFindIndex = require('array-find-index');
arrayFindIndex(['rainbow', 'unicorn', 'pony'], x => x === 'unicorn');
//=> 1
`
Same as Array#findIndex()`, but with the input array as the first argument.
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