Formik: Add generics to ArrayHelpers type

[nzacca]

Current Behavior

The current ArrayHelpers type does not use generics in its type.

Desired Behavior

It would be nice if the ArrayHelpers added generics so that we could type check the inner methods as well.

Suggested Solution

export type FieldArrayRenderProps<T = any, Values = any> = ArrayHelpers<T> & {
  form: FormikProps<Values>;
  name: string;
};

interface ArrayHelpers<T = any> {
  push: (obj: T) => void;
  handlePush: (obj: T) => () => void;
  swap: (indexA: number, indexB: number) => void;
  handleSwap: (indexA: number, indexB: number) => () => void;
  move: (from: number, to: number) => void;
  handleMove: (from: number, to: number) => () => void;
  insert: (index: number, value: T) => void;
  handleInsert: (index: number, value: T) => () => void;
  replace: (index: number, value: T) => void;
  handleReplace: (index: number, value: T) => () => void;
  unshift: (value: T) => number;
  handleUnshift: (value: T) => () => void;
  handleRemove: (index: number) => () => void;
  handlePop: () => () => void;
  remove(index: number): T | undefined;
  pop(): T | undefined;
}

Who does this impact? Who is this for?

• No impact if we use defaults for the generics
• Allows users to strongly type the arrayHelpers prop if desired.

I'm willing to submit a PR for this if this sounds ok.

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[nzacca]

@jaredpalmer just wondering if this is something you'd like me to work on. Happy to do it (or not do it). 😄

[IronSean]

I also would like this. Currently I'm trying to figure out some type hijinks to force form to have the type of the form to get type checking when I access it within my FieldArray block, or just passing the form prop down from the outer Formik render prop because it's typed. But neither as as ideal as just being able to type the arrayHelpers.

I was coming here to offer to make my own PR about this issue, but found this currently existing. I know you're in the thick of v2 prep but let me or @nzacca know if you'd like a PR for this @jaredpalmer

[IronSean]

Made a PR at https://github.com/jaredpalmer/formik/pull/1982