Use findIndex, but start looking in a specific position

Question

I have the following extract of code:

private getNextFakeLinePosition(startPosition: number): number{
        return this.models.findIndex(m => m.fakeObject);
}

This function returns me the index of the first element which has the property fakeObject with the true value.

What I want is something like this, but instead of looking for the all items of the array, I want to start in a specific position (startPosition).

Note: This is typescript but the solution could be in javascript vanilla.

Thank you.

Answer 1

The callback to findIndex() receives the current index, so you could just add a condition that way:

private getNextFakeLinePosition(startPosition: number): number {
    return this.models.findIndex((m, i) => i >= startPosition && m.fakeObject);
}

Not the most efficient solution, but should be OK as long as your array is not too large.

Answer 2

You can try with slice:

private getNextFakeLinePosition(startPosition: number): number {
  const index = this.models.slice(startPosition).findIndex(m => m.fakeObject);
  return index === -1 ? -1 : index + startPosition;
}

It'll slice your input array and find the index on a subarray. Then - at the end, just add the startPosition to get the real index.

Answer 3

A vague, but working solution would be to skip the indices until we reach the start index:

let startIndex = 4;
array.findIndex((item, index) => index >= 4 && item.fakeObject);