# Index

| type   | returns  |
| ------ | -------- |
| method | `number` |

## Arguments

| name   | type   | description                 |
| ------ | ------ | --------------------------- |
| needle | string | The substring to search for |

## Explanation

Returns the index of the start of the `substring` in the given string. Returns `-1` if not found.

## Examples

```swift
"Hello! Hi!".index("Hi") == 7
"Goats :D".index("Hi") == -1
```