[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [arrayBinaryIndexOf](./rc-js-util.arraybinaryindexof.md) ## arrayBinaryIndexOf() function Performs a bisection search of an 'indexable' object, i.e. can be accessed by index, for example `Array`. Custom data structures are also supported. **Signature:** ```typescript export declare function arrayBinaryIndexOf(indexable: T, comparisonValueToSearchFor: number, getComparisonValueAtIndex: TGetComparisonValueAtIndex, length: number, start?: number): number; ``` ## Parameters

Parameter	Type	Description
indexable	T	The thing to be searched. This must be sorted ascending.
comparisonValueToSearchFor	number	The comparison value which is being searched for.
getComparisonValueAtIndex	[TGetComparisonValueAtIndex](./rc-js-util.tgetcomparisonvalueatindex.md)<T>	A function that provides the value for comparison at a given index.
length	number	The number of elements in the structure `indexable` to search.
start	number	_(Optional)_ The start index.

**Returns:** number The index of the searched for item, else -1 if it cannot be found. ## Remarks The `indexable` parameter must be sorted ascending. Where there are multiple equal values the lowest index will be returned. See [arrayBinaryIndexOf()](./rc-js-util.arraybinaryindexof.md). ## Example ```typescript // searching for the number 3 with start index 1 & length 2 const index = arrayBinaryIndexOf([1, 2, 3, 4], 3, (a, i) => a[i], 2, 1); // index is 2 ```