[Home](./index.md) > [rc-js-util](./rc-js-util.md) > [arrayBinaryFindInsertionIndex](./rc-js-util.arraybinaryfindinsertionindex.md) ## arrayBinaryFindInsertionIndex() function Performs a bisection search of an 'indexable' object such that if the value were inserted, it would remain in order. **Signature:** ```typescript export declare function arrayBinaryFindInsertionIndex(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 to find the insertion index 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 to insert the element at, the highest value is the length of the array. ## Remarks The `indexable` parameter must be sorted ascending. Where there are multiple equal values the lowest index will be returned. ## Example ```typescript // searching for the number 2.5 with start index 1 & length 2 const index = arrayBinaryFindInsertionIndex([1, 2, 3, 4], 2.5, (a, i) => a[i], 2, 1); // index is 2 ```