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array.lastIndexWhere()

Get the index of the last Array element that matches a provided predicate.

Signature

lastIndexWhere(predicate: (A => Boolean | Null)) => Number | Null

lastIndexWhere(predicate: A => Boolean | Null, end: Number) => Number | Null

Description

Searches, right-to-left, for the first element that matches a provided predicate function and returns the index of the element if a match is found.

If the optional start index is provided, the method searches right-to-left starting at index and returns the first matching index (inclusive).

Parameters

Parameter Type Required Description

predicate

Function

Yes

Anonymous predicate function that:

  • Accepts an Array element as its only argument. You can pass in this argument using arrow function syntax.

  • Returns Boolean or Null.

If the predicate evaluates to true for an element, the element is considered a match.

end

Number

Starting index (inclusive) of the right-to-left search. Must be an Int.

Return value

One of:

Type Description

Number

Index of the element that matches the provided predicate.

Null

Returned if a match isn’t found.

Examples

['a', 'b', 'c', 'b'].lastIndexWhere(v => v == 'b')
3

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