evolve-ts
v2.2.0
Published
Immutably update nested objects with patches containing values or functions to update values
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evolve-ts
npm install evolve-ts
Immutably update nested objects with patches containing values or functions to update values
- Simple yet powerful: simple syntax for performing immutable updates
- Type-safe: Robust type checking and type inferences
- Tiny: < 1kb gzipped, zero dependencies
Usage
Let's say we have the following state
import { evolve, unset } from "evolve-ts"
const state = {
user: {
name: "Alice",
age: 22
}
}
We can set a value
evolve({ user: { name: "Bob" } }, state)
// { user: { name: "Bob", age: 22 } }
Update a value
evolve({ user: { age: age => age + 1 } }, state)
// { user: { name: "Alice", age: 23 } }
Remove a key
evolve({ user: { age: unset } }, state)
// { user: { name: "Alice" } }
All together now!
import { evolve, unset } from "evolve-ts"
const alice = {
name: "Alice",
age: 22,
active: true,
likes: ["wonderland"],
nested: {
foo: true,
bar: true,
}
}
evolve({
name: "Bob", // sets the value of name
age: age => age + 1, // updates the value of age
active: unset, // removes the active key
likes: ["building"], // sets the value of likes (only objects are merged)
nested: {
foo: false // sets the value of foo
}
}, alice)
/*
{
name: "Bob",
age: 23,
likes: ["building"],
nested1: {
foo: false,
bar: true,
}
}
*/
Setting object values directly
Object values are merged recursively, but return values of functions are set directly. To replace an object value use a constant
function.
evolve({
user: () => ({
name: "Bob",
age: 33,
})
}, state)
// { user: { name: "Bob", age: 33 } }
Removing object entries
Entries can be removed by setting the value to unset
or using an updater function that returns unset
.
evolve({
user: {
name: unset,
age: () => unset
}
}, state)
// { user: {} }
Working with Arrays
evolve-ts provides two functions to update arrays, map
and adjust
.
map
is a version of the map function that can either take a callback or a patch. The following are all equivalent, they all increment the number of likes for each user in the users array.
import { map } from "evolve-ts"
const inc = n => n + 1
map({ likes: inc })(users)
map(evolve({ likes: inc }))(users)
map(user => ({ ...user, likes: inc }))(users)
adjust
conditionally maps values with a callback function or patch. Value(s) to map can be specified with an index or predicate function. Negative indexes are treated as offsets from the array length.
import { adjust } from "evolve-ts"
// set the first user as preferred
adjust(0, { preferred: true })(users)
// set the last user as preferred
adjust(-1, { preferred: true })(users)
// set all users who have 100 or more likes as preferred
adjust(user => user.likes > 99, { preferred: true })(users)
// like map, can also take a callback to update the value
adjust(0, user => ({ ...user, preferred: true }))(users)
Other array helpers such as append
and filter
are not re-implemented by evolve-ts as they are already included in fp-ts, Ramda, and many other libraries.
import { adjust, evolve, map } from "evolve-ts"
import { append, filter, inc } from "" // your favorite functional utility library
const state = {
users: [
{ name: "Alice", age: 22, id: 0 },
{ name: "Bob", age: 33, id: 1 }
]
}
// add a new user
evolve({
users: append({ name: "Claire", age: 44, id: 2 })
}, state)
// increment the ages of all users
evolve({
users: map({ age: inc })
}, state)
// set the age of a user by id
evolve({
users: adjust(user => user.id === 1, { age: 55 })
}, state)
// remove a user by id
evolve({
users: filter(user => user.id !== 1)
}, state)
Currying
import { evolve } from "evolve-ts"
const incrementAge = evolve({ age: age => age + 1 })
incrementAge({ name: "Alice", age: 22 })
// { name: "Alice", age: 23 }
TypeScript Support
The evolve
function is strictly typed and does not allow polymorphism. The return type is always the same as the target type.
import { evolve, unset } from "evolve-ts"
// cannot change the type of values in target
evolve({ age: "22" }, { name: "Alice", age: 22 })
// TypeError: Type 'string' is not assignable to type 'number | ((value: number) => number)'
// updaters have correctly inferred types (updater argument in this example is inferred as number)
evolve({ age: age => age + 1 }, { name: "Alice", age: 22 })
// ReturnType: { name: string; age: number; }
// unset can be used on optional keys
evolve({ age: unset }, { name: "Alice", age: 22 } as { name: string; age?: number; })
// ReturnType: { name: string; age?: number; }
// unset cannot be used on required keys
evolve({ age: unset }, { name: "Alice", age: 22 })
// TypeError: Type 'typeof Unset' is not assignable to type 'number | ((value: number) => number)'
// cannot add extraneous properties to the patch
evolve({ name: "Alice", age: 23 }, { age: 22 })
// TypeError: ...'name' does not exist in type 'Patch<{ age: number; }>'
// cannot set non-nullable properties to undefined when exactOptionalPropertyTypes is enabled
evolve({ name: undefined }, { name: "Alice" })
// Type 'undefined' is not assignable to type 'string | ((value: string) => string)'
The evolve_
function is a type alias for evolve
that allows polymorphism while still producing strongly typed results.
import { evolve_, unset } from "evolve-ts"
// changing age from number to string
evolve_({ age: "22" }, { name: "Alice", age: 22 })
// ReturnType: { name: string; age: string; }
// adding name key
evolve_({ name: "Alice", age: 23 }, { age: 22 })
// ReturnType: { name: string, age: number; }
// adding age key with updater function
evolve_({ age: (): number => 22 }, { name: "Alice" })
// ReturnType: { name: string, age: number; }
// removing age key
evolve_({ age: unset }, { name: "Alice", age: 22 })
// ReturnType: { name: string; }
Shallow Updates
The behavior of shallowEvolve
is similar to the spread operator except it accepts updater functions.
import { evolve, shallowEvolve } from "evolve-ts"
declare const user
shallowEvolve({ user }) /* equivalent to */ evolve({ user: () => user })
// evolve can be used within shallowEvolve if a deep merge is needed for a particular key
shallowEvolve({ user: evolve(user) }) /* equivalent to */ evolve({ user })
Provided Functions
evolve
: Takes a patch object and a target object and returns a version of the target object with updates from the patch applied. A patch is a subset of the target object containing either values or functions to update values. Functions are called with existing values from the target, non-object values are set into the target, and object values are merged recursively.evolve_
: Type alias for evolve that allows polymorphism while still producing strongly typed results.map
: Maps values in an array with a callback function or patch.adjust
: Conditionally maps values in an array with a callback function or patch. Value(s) to map can be specified with an index or predicate function. Negative indexes are treated as offsets from the array length.unset
: Sentinel value that causes its key to be removed from the output.shallowEvolve
: Likeevolve
but performs shallow updates.shallowMap
: Likemap
but performs shallow updates.shallowAdjust
: Likeadjust
but performs shallow updates.
Why evolve-ts?
evolve-ts was created as a lightweight alternative to updeep and immer. It has all of updeep's core functionality, strong TypeScript support, is only a fraction of the size of updeep or immer, and is dependency free.
Caveats
evolve-ts treats all functions in patches as updater functions, so if your state contains function values you want to update you must wrap the updates in a constant
function.
import { evolve } from "evolve-ts"
const state = {
name: "Alice",
greet: (person) => console.log(`Hi ${person} I'm Alice!`)
}
// need to use a wrapper to set new function values
evolve({
name: "Bob",
greet: () => (person) => console.log(`Hi ${person} I'm Bob!`)
}, state)
License
MIT