I am working on a piece of JS code. In a tutorial I found a piece of code I don't understand:

const position = this.quotes.findIndex((quoteEl: Quote) => {
  return quoteEl.id == quote.id;
});

I think the person who wrote the code stuffed a lot of different pieces into this line. Can somebody help me bring that into a more "easy to understand" form?

For example, the argument of the findIndex method can probably written in a separate function, right?

Thanks, Benjamin

I am working on a piece of JS code. In a tutorial I found a piece of code I don't understand:

const position = this.quotes.findIndex((quoteEl: Quote) => {
  return quoteEl.id == quote.id;
});

I think the person who wrote the code stuffed a lot of different pieces into this line. Can somebody help me bring that into a more "easy to understand" form?

For example, the argument of the findIndex method can probably written in a separate function, right?

Thanks, Benjamin

• javascript
• typescript

• findIndex implementation would be something like : Loop through the array, pass each element to the callback passed and check the response. If its true, break the loop and return the index of element otherwise send a default value preferably -1 – binariedMe Commented Jun 20, 2017 at 19:28
• 2 The Array.prototype.findIndex() is taking a custom parison function, and returning the index of the first true it finds, the => is an Arrow Function – Patrick Barr Commented Jun 20, 2017 at 19:35

1 Answer 1

findIndex calls the passed function with each element of the array and returns the index of the first element that returned true, or -1 if none did.

This is your callback function

(quoteEl: Quote) => {
  return quoteEl.id == quote.id;
}