_.findIndex() always return -1 (lodash.js)

Question

I'm working with a javascript project. I'm trying to use lodash tool to make life easier. I'd like to find a value in array if it exist. So, I select a findIndex() function. https://lodash.com/docs/4.17.15#findIndex

It's document says that the function will

Returns the index of the found element, else -1.

Then, I tried

console.log( _.findIndex([7,8,9], 7) );

The result is always -1

I think I did like the example already but I got only -1.

Please someone help.

Answer 1

The second parameter is [predicate=_.identity] (Function): The function invoked per iteration. So you have to pass expression instead of value . Try like below.

console.log(_.findIndex([7,8,9], x => x === 7));

 console.log(_.findIndex([7,8,9], x => x === 7));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js" integrity="sha256-VeNaFBVDhoX3H+gJ37DpT/nTuZTdjYro9yBruHjVmoQ=" crossorigin="anonymous"></script>

Answer 2

Why not use ES6 built in functions, instead of importing a library

const index = [7, 8, 9].findIndex(x => x === 7);

console.log(index);