Array.prototype.findIndex ES6 polyfill for ES5 versions and lower via NPM, you only need to require the module in order to have it working in order to use knowing that is going to work in browsers that does not support this function natively.

- Based from Mozilla polyfill.

1. Require the npm module.

npm install --save-dev jspolyfill-array.prototype.findIndex

2. Include the file before the usage.

Then you need to require the file on your main.js or where you are going to plan to use the find function as follows:

require("jspolyfill-array.prototype.findIndex")

arr.findIndex(callback[, thisArg])

Where arr is your array.

• callback Function to execute on each value in the array, taking three arguments:
  • element The current element being processed in the array.
  • index The index of the current element being processed in the array.
  • array The array findIndex was called upon.
• thisArg Optional. Object to use as this when executing callback.

The callback passed as a parameter inside of the findIndex function is fired every time per each element inside of the array until finds an element where the callback evaluates to true.

It returns the index of the first match otherwise if no match is found it will return -1.

For more information click here.