Return index value from filter method javascript

The .findIndex() method returns the index of the first element of the array that satisfies a condition given by a function. If the function returns false for all elements of the array, the result is -1.

See the documentation here.

In my example, x is an item for each iteration and I use cross function for my condition.

const datas = [];
const fieldId = 5;
let index = datas.findIndex( x => x.Id === fieldId );