In 12. implement Immutability helper, we are asked to implement immutability helpers.

These helpers requires extra effort for us to remember how to use them, while Immer takes another approach which might be easier to use.

For example, we have a base state as below.

const state = [
  {
    name: 'BFE',
  },
  {
    name: '.',
  }
]

We can use produce() to patch our modification and get a new state.

const newState = produce(state, draft => {
  draft.push({name: 'dev'})
  draft[0].name = 'bigfrontend'
  draft[1].name = '.' // set with the same value
})

Unchanged parts are not cloned.

expect(newState).not.toBe(state);
expect(newState).toEqual(
  [
    {
      name: 'bigfrontend',
    },
    {
      name: '.',
    },
    {
      name: 'dev'
    }
  ]
);
expect(newState[0]).not.toBe(state[0])
expect(newState[1]).toBe(state[1])
expect(newState[2]).not.toBe(state[2])

Please implement your produce().

This is not to recreate Immer, test cases only cover the basic usage.
You only need to support basic usage on plain object and array, things like Map/Set, Auto freezing .etc are out of scope.
You need to make sure unchanged parts are not cloned.

Watch videos for JavaScript Coding Question 164. implement Immer produce()

Watch videos for JavaScript Coding Question
164. implement Immer produce()