Support $ReadOnlyArray

This is a:

• Bug Report
• Feature Request
• Question
• Other

Which concerns:

• flow-runtime
• babel-plugin-flow-runtime
• flow-runtime-validators
• flow-runtime-mobx
• flow-config-parser
• The documentation website

---

type Thing = $ReadOnlyArray<string | number>;

const thing: Thing = [];

console.log(thing);

Output:

Thing must be an object

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

Actual Value: []

Actual Type: Array<any>

no errors with flow

---

IssueHunt Summary

Backers (Total: $40.00)

• issuehunt ($40.00)

Submitted pull Requests

• #236 Initial support for $ReadOnlyArray

---

Become a backer now!

Or submit a pull request to get the deposits!

Tips

• Checkout the Issuehunt explorer to discover more funded issues.
• Need some help from other developers? Add your repositories on IssueHunt to raise funds.

---

IssueHunt has been backed by the following sponsors. Become a sponsor

[jedwards1211]

I think the only 100% solid approach is for the Babel plugin to add code to any index assignments, length assignments, or function calls on the $ReadOnlyArray identifier

[jedwards1211]

That’s probably true, actually a problem with proxy or copy approach is that neither is === the original array