Function findFirstIndex

findFirstIndex<T>(array, fn, start?, stop?): number
Find the index of the first value which matches a predicate.
Type Parameters
- T
Parameters
- array: ArrayLike<T>
  
  The array-like object to search.
- fn: ((value, index) => boolean)
  
  The predicate function to apply to the values.
  - - (value, index): boolean
    - Parameters
      
      value: T
      
      index: number
      
      Returns boolean
- start: number = 0
  
  The index of the first element in the range to be searched, inclusive. The default value is 0. Negative values are taken as an offset from the end of the array.
- stop: number = -1
  
  The index of the last element in the range to be searched, inclusive. The default value is -1. Negative values are taken as an offset from the end of the array.
Returns number
The index of the first matching value, or -1 if no matching value is found.

Notes
If stop < start the search will wrap at the end of the array.

Complexity
Linear.

Undefined Behavior
A start or stop which is non-integral.

Modifying the length of the array while searching.

Example
```
import { ArrayExt } from '@lumino/algorithm';

function isEven(value: number): boolean {
  return value % 2 === 0;
}

let data = [1, 2, 3, 4, 3, 2, 1];
ArrayExt.findFirstIndex(data, isEven);       // 1
ArrayExt.findFirstIndex(data, isEven, 4);    // 5
ArrayExt.findFirstIndex(data, isEven, 6);    // -1
ArrayExt.findFirstIndex(data, isEven, 6, 5); // 1
```
- Defined in packages/algorithm/src/array.ts:209

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