# checkValidIndex method

void checkValidIndex (int index, dynamic indexable, [ String name, int length, String message ])

Check that a value is a valid index into an indexable object.

Throws if `index` is not a valid index into `indexable`.

An indexable object is one that has a `length` and a and index-operator `[]` that accepts an index if `0 <= index < length`.

If `length` is provided, it is used as the length of the indexable object, otherwise the length is found as `indexable.length`.

## Implementation

    static void checkValidIndex(int index, var indexable,
        [String name, int length, String message]) {
      if (length == null) length = indexable.length;
      // Comparing with `0` as receiver produces better dart2js type inference.
      if (0 > index || index >= length) {
        if (name == null) name = "index";
        throw new RangeError.index(index, indexable, name, message, length);
      }
    }