simple-update-in

simple-update-in

A lightweight updateIn for immutable objects.

We love ImmutableJS. But sometimes, we want to start something from small. Thus, we created this package with zero dependencies.

Under the cover, we use Rest Operator to do most of the heavylifting.

Install

For latest stable, run npm install simple-update-in.

For active development (master branch), run npm install simple-update-in@master.

How to use

For example, obj.one.two = 1.2, call updateIn(obj, ['one', 'two'], 1.2). It will return a new object with changes in deep clone.

We share similar signature as ImmutableJS.updateIn:

updateIn<T: Array|Map>(
  target: T,
  path: (Number|String)[],
  updater?: (value: any) => any
): T

To make updateIn efficient, especially, when paired with React. It will return a mixed deep/shallow clone of the target. It only deep clone on objects that it modified along the path, and shallow clone objects that it did not modify.

Like other immutable framework, updater is expected to return a new object if there is a change. If the update do not result in a change (triple-equal ===), then, the original object is returned.

Example

Just like ImmutableJS, we want to make both Array and Map a first-class citizen. To work on a map, use a string as key. For arrays, use a number as key.

Map

import updateIn from 'simple-update-in';

const from = { one: 1, two: { number: 2 }, thirty: 3 };
const actual = updateIn(from, ['thirty'], three => three * 10);

expect(actual).toEqual({ one: 1, two: { number: 2 }, thirty: 30 });

expect(actual).not.toBe(from);   // Something under this tree has changed
expect(actual.two).toBe(to.two); // Nothing under this tree has changed
expect(actual.thirty).toBe(30);  // We multiplied it by 10

This is in fact an "upsert" operation.

Array in map

const from = { one: [1.1, 1.2, 1.3], two: [2] };
const actual = updateIn(from, ['one', 1], value => 'one point two');

expect(actual).toEqual({ one: [1.1, 'one point two', 1.3], two: [2] });

Remove a key

You can also use updateIn to remove a key by passing a falsy value to the updater argument, or return undefined.

const from = { one: 1, two: 2 };
const actual = updateIn(from, ['two']);

expect(actual).toEqual({ one: 1 });

expect(actual).not.toBe(from);
expect(actual).not.toHaveProperty('two');

When removing a non-existing key, the original object will be returned.

The sample code above also works with updater returning undefined, for example, updateIn(from, ['two'], () => undefined).

Remove an item in array

const from = ['zero', 'one', 'two'];
const actual = updateIn(from, [1]);

expect(actual).toEqual(['zero', 'two']);

Also for updater returning undefined

Automatic expansion

const from = {};
const actual = updateIn(from, ['one', 'two'], 1.2);

expect(actual).toEqual({ one: { two: 1.2 } });

If the updater return undefined, the object will be untouched.

Replace incompatible types

If incompatible types is found along the walk, they will be replaced. For example, in the following example, an Array is replaced by a Map.

const from = [0, 1, 2];
const actual = updateIn(from, ['one'], 1);

expect(actual).toEqual({ one: 1 });

In the path, 'one' is a string, it implies that user want a Map instead of Array

It will also replace number with Map.

const from = { one: 1 };
const actual = updateIn(from, ['one', 'two'], 1.2);

expect(actual).toEqual({ one: { two: 1.2 } });

Corner case

If the target value is of incompatible type, we will convert it to correct type before setting it. In the following sample, the actual value is an empty map instead of the original array.

const from = [0, 1, 2];
const actual = updateIn(from, ['one']);

expect(actual).toEqual({});

Adding an item to array

You can use special index value -1 to indicate an append to the array.

const from = [0, 1];
const actual = updateIn(from, [-1], () => 2);

expect(actual).toEqual([0, 1, 2]);

If updater returned undefined, the value will not be appended.

There is no support on prepend or insertion, however, you can use Rest Operator for array manipulation.

const from = { numbers: ['one', 'two'] };
const actual = updateIn(from, ['numbers'], array => ['zero', ...array]);

expect(actual).toEqual({ numbers: ['zero', 'one', 'two'] });

Using predicate

For path accessor, instead of number and string, you can also use function.

Predicate for array has signature of (value, index) => truthy/falsy. And for map, (value, key) => truthy/falsy.

const from = [1, 2, 3, 4, 5];
const actual = updateIn(from, [value => value % 2], value => value * 10);

expect(actual).toEqual([10, 2, 30, 4, 50]);

Branching with predicate

You can also use predicate to update multiple subsets at the same time.

const from = [{ v: 1 }, { v: 2 }, { v: 3 }];
const actual = updateIn(from, [() => true, 'v'], v => v * 10);

expect(actual).toEqual([{ v: 10 }, { v: 20 }, { v: 30 }]);

Non-existing key/index with predicate

Since it is impossible to guess if the predicate is performing on an array or map. automatic expansion will not be performed if the key/index does not exists. Nevertheless, even we expand it into an empty array or map, it will not be enumerated thru the predicate since the new item is empty. Thus, nothing will change.

const from = {};
const actual = updateIn(from, ['Hello', () => true], () => 'World!']);

expect(actual).toBe(from);

const from = [];
const actual = updateIn(from, [0, () => true], () => 'Aloha']);

expect(actual).toBe(from);

Contributions

Like us? Star us.

Want to make it better? File us an issue.

Don't like something you see? Submit a pull request.

Changelog

[1.4.0] - 2018-10-08

Changed

• Add default exports for CommonJS
• Bump
  • @babel/core@7.1.2
  • merge@1.2.1 (via npm audit fix)
  • jest@23.6.0