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

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);

Answer 3

Really old one but the easiest way would probably be

const startingIndex = 1;
[
  {label: 'a'},
  {label: 'b'}
]
.slice(startingIndex)
.findIndex(({ label }) => 
  label.toLowerCase().startsWith(labelToFinds.toLowerCase())
)

Answer 4

In this case i would probably use for loop. It doesn't add overhead to slice array and avoids unnecessary indices check.

const findStartFromPos = <T>(predicate: (e: T) => boolean, array: T[], startFrom: number): number => {
  for (let i = startFrom; i < array.length; i++) {
    if (predicate(array[i])) {
      return i;
    }
  }

  return -1;
};