isDraftable()

isDraftable(value, options?) returns true for a value that Mutative can draft, and which create() therefore accepts as its base state.

isDraftable(value: any, options?: { mark?: Mark }): boolean

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import { isDraftable } from 'mutative';

const baseState = {
  date: new Date(),
  list: [{ text: 'todo' }],
};

expect(isDraftable(baseState)).toBe(true);
expect(isDraftable(baseState.list)).toBe(true);
expect(isDraftable(baseState.date)).toBe(false);

Without a mark, these values are draftable:

• Plain objects, whose prototype is Object.prototype.
• Arrays.
• Map and Set instances, also of their subclasses.

Other values are not: primitives, functions, dates, class instances, objects without a prototype, and plain objects of other realms, such as iframes. A mark makes them draftable, as markSimpleObject() does for objects without a prototype and plain objects of other realms. Pass the same mark that the create() calls use, to get their answer:

import { isDraftable } from 'mutative';

class Todo {
  constructor(public text: string) {}
}

const mark = (target: unknown) =>
  target instanceof Todo ? ('immutable' as const) : undefined;

expect(isDraftable(new Todo('learn'))).toBe(false);
expect(isDraftable(new Todo('learn'), { mark })).toBe(true);

A mark makes a value draftable when it returns 'immutable' or a function that copies the value. A mark that returns 'mutable' keeps a value out of drafts when a recipe reads it, but isDraftable() still returns true for plain objects, arrays, Maps and Sets.