Support $ReadOnlyArray

[](https://oss.issuehunt.io/r/gajus/flow-runtime/issues/199)

This is a:

- [ ] Bug Report
- [x] Feature Request
- [ ] Question
- [ ] Other

Which concerns:

- [x] flow-runtime
- [ ] babel-plugin-flow-runtime
- [ ] flow-runtime-validators
- [ ] flow-runtime-mobx
- [ ] flow-config-parser
- [ ] The documentation website

---

```
type Thing = $ReadOnlyArray;

const thing: Thing = [];

console.log(thing);
```

Output:

```
Thing must be an object

Expected: {
[Symbol(Symbol.iterator)]: () => Iterator;
toLocaleString: () => string;
concat: | S> (...items: Array) => Array;
entries: () => Iterator<[number, T]>;
every: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => boolean;
filter: ((callbackfn: Boolean) => Array<$NonMaybeType>) | ((callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => Array);
find: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => T | void;
findIndex: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => number;
forEach: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => void;
includes: (searchElement: mixed, fromIndex?: number) => boolean;
indexOf: (searchElement: mixed, fromIndex?: number) => number;
join: (separator?: string) => string;
keys: () => Iterator;
lastIndexOf: (searchElement: mixed, fromIndex?: number) => number;
map: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => U, thisArg?: any) => Array;
reduce: ((callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: $ReadOnlyArray) => T, initialValue: void) => T) | ( (callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: $ReadOnlyArray) => U, initialValue: U) => U);
reduceRight: ((callbackfn: (previousValue: T, currentValue: T, currentIndex: number, array: $ReadOnlyArray) => T, initialValue: void) => T) | ( (callbackfn: (previousValue: U, currentValue: T, currentIndex: number, array: $ReadOnlyArray) => U, initialValue: U) => U);
slice: (start?: number, end?: number) => Array;
some: (callbackfn: (value: T, index: number, array: $ReadOnlyArray) => any, thisArg?: any) => boolean;
values: () => Iterator;
length: number;
[key: number]: T;
}

Actual Value: []

Actual Type: Array
```

[no errors with flow](https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVAXAngBwKZgAqAFgJYB2A5mALxgAkASngIYAmA8uTFgIIBO-FlgA8AZwz8K1AD5hyAVwC2AIzz8AfAG50AYzjkJYDGSoAuIqep0A2gF0dqfYbgw8AOniUAFCekBKLSA)

---

IssueHunt Summary

### Backers (Total: $40.00)

- [ issuehunt](https://oss.issuehunt.io/u/issuehunt) ($40.00)

### Submitted pull Requests
- [#236 Initial support for $ReadOnlyArray](https://oss.issuehunt.io/r/gajus/flow-runtime/pull/236)
- [#300 feat: support generic conversion](https://oss.issuehunt.io/r/gajus/flow-runtime/pull/300)
---

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Start with the failing $ReadOnlyArray example and review submitted pull requests #236 and #300 to understand the existing implementation direction. Done means the example no longer reports the array as an object and runtime validation accepts the Flow type shown.

Written by the indexing model from the issue text.