react-state-mutations

State updates in React may be asynchronous. In the case that you're using the previous state to calculate the next state, you could run into race conditions when React attempts to batch your state changes together. The following example demonstrates the problem:

// Warning! This is the bad example.
import React, { Component } from "react";
 
class Counter extends Component {
  constructor(props) {
    super(props);
 
    this.state = { count: 0 };
    this.handleClick = this.handleClick.bind(this);
  }
 
  handleClick() {
    this.setState({ count: this.state.count + 1 });
    this.setState({ count: this.state.count + 1 });
  }
 
  render() {
    const { count } = this.state;
    return (
      <button type="button" onClick={this.handleClick}>
        {count}
      </button>
    );
  }
}
 
export default Counter;

In the example above, since both setState calls mutate the same key, those mutations can be merged together, and you may end up with it only incrementing each click by one since the last mutation will win. You can solve this by passing a function to setState, as those are executed sequentially and will not run over each other. This is demonstrated in the example below:

import React, { Component } from "react";
 
class Counter extends Component {
  constructor(props) {
    super(props);
 
    this.state = { count: 0 };
    this.handleClick = this.handleClick.bind(this);
  }
 
  handleClick() {
    this.setState(({ count }) => ({ count: count + 1 }));
    this.setState(({ count }) => ({ count: count + 1 }));
  }
 
  render() {
    const { count } = this.state;
    return (
      <button type="button" onClick={this.handleClick}>
        {count}
      </button>
    );
  }
}
 
export default Counter;

The beauty of this approach is that you can begin to extract out the state mutation into a separate function that can then be reused. As in the following refactor:

import React, { Component } from "react";
 
const incrementCount = ({ count }) => ({ count: count + 1 });
 
class Counter extends Component {
  constructor(props) {
    super(props);
 
    this.state = { count: 0 };
    this.handleClick = this.handleClick.bind(this);
  }
 
  handleClick() {
    this.setState(incrementCount);
    this.setState(incrementCount);
  }
 
  render() {
    const { count } = this.state;
    return (
      <button type="button" onClick={this.handleClick}>
        {count}
      </button>
    );
  }
}
 
export default Counter;

This is the basis for this library. The increment function is already defined for you, as well as various other utilities. This library additionally provides an easy interface for defining your own mutations that read from the previous state so that you never run into race conditions with your state mutations. Using react-state-mutations, the final result would look like:

import React, { Component } from "react";
import { increment } from "react-state-mutations";
 
const incrementCount = increment("count");
 
class Counter extends Component {
  constructor(props) {
    super(props);
 
    this.state = { count: 0 };
    this.handleClick = this.handleClick.bind(this);
  }
 
  handleClick() {
    this.setState(incrementCount);
    this.setState(incrementCount);
  }
 
  render() {
    const { count } = this.state;
    return (
      <button type="button" onClick={this.handleClick}>
        {count}
      </button>
    );
  }
}
 
export default Counter;

You can alternatively use this library in conjunction with the useState feature in React. To get the equivalent as the above example working, you can use:

import React, { useState } from "react";
import { incrementState } from "react-state-mutations";
 
const Counter = () => {
  const [count, setCount] = useState(0);
  const onClick = () => {
    setCount(incrementState);
    setCount(incrementState);
  };
 
  return (
    <button type="button" onClick={onClick}>
      {count}
    </button>
  );
};
 
export default Counter;

Or, you could use the built in useIncrement hook, as in:

import React from "react";
import { useIncrement } from "react-state-mutations";
 
const Counter = () => {
  const [count, onIncrement] = useIncrement(0);
  const onClick = () => {
    onIncrement();
    onIncrement();
  };
 
  return (
    <button type="button" onClick={onClick}>
      {count}
    </button>
  );
};
 
export default Counter;

Getting started

Install this package through npm (npm install react-state-mutations --save) or yarn (yarn add react-state-mutations). You can then import and use the mutations from within your components.

In addition with the ability to create your own mutations, this package ships with some pre-built mutations, listed below.

• append
• concat
• cycle
• decrement
• direct
• filter
• increment
• map
• mutate
• prepend
• toggle

There is also an equivalent version of each of these mutations that works on standalone values. This can be used in conjunction with React's useState to manipulate state in a safe way. The equivalent version is named the same, with State appended onto the end. i.e., the equivalent mutation for toggle is toggleState, which will effectively perform value => !value. Finally, there are hooks built in that use those mutations, so in useToggle for the above example.

append

Appends a value to a list, as in the example:

import { append } from "react-state-mutations";
 
const appendStudent = append("students");
 
const prevState = { students: [{ name: "Harry" }, { name: "Hermione" }] };
const nextState = appendStudent({ name: "Ron" })(prevState);
// => { students: [{ name: "Harry" }, { name: "Hermione" }, { name: "Ron" }] }

With single values:

import { appendState } from "react-state-mutations";
 
const prevState = [{ name: "Harry" }, { name: "Hermione" }];
const nextState = appendState({ name: "Ron" })(prevState);
// => [{ name: "Harry" }, { name: "Hermione" }, { name: "Ron" }]

With hooks:

import { useAppend } from "react-state-mutations";
 
const Students = () => {
  const [students, onAppend] = useAppend([
    { name: "Harry" },
    { name: "Hermione" }
  ]);
 
  // sometime later...
  onAppend({ name: "Ron" });
};

With TypeScript, append, appendState, and useAppend all accept an additional type argument for specifying which type the array will hold, as in:

interface Student {
  name: string;
}
 
append<Student>("students");

concat

Concatentate two lists, as in the example:

import { concat } from "react-state-mutations";
 
const concatStudents = concat("students");
 
const prevState = { students: [{ name: "Harry" }, { name: "Hermione" }] };
const nextState = concatStudents([{ name: "Ron" }, { name: "Ginny" }])(
  prevState
);
// => { students: [{ name: "Harry" }, { name: "Hermione" }, { name: "Ron" }, { name: "Ginny" }] }

With single values:

import { concatState } from "react-state-mutations";
 
const prevState = [{ name: "Harry" }, { name: "Hermione" }];
const nextState = concatState([{ name: "Ron" }, { name: "Ginny" }])(prevState);
// => [{ name: "Harry" }, { name: "Hermione" }, { name: "Ron" }, { name: "Ginny" }]

With hooks:

import { useConcat } from "react-state-mutations";
 
const Students = () => {
  const [students, onConcat] = useConcat([
    { name: "Harry" },
    { name: "Hermione" }
  ]);
 
  // sometime later...
  onConcat([{ name: "Ron" }, { name: "Ginny" }]);
};

With TypeScript, concat, concatState, and useConcat all accept an additional type argument for specifying which type the array will hold, as in:

interface Student {
  name: string;
}
 
concat<Student>("students");

cycle

Cycles through a list of values, as in the example:

import { cycle } from "react-state-mutations";
 
const cycleHouse = cycle("house");
const visitNextHogwartsHouse = cycleHouse([
  "Gryffindor",
  "Hufflepuff",
  "Ravenclaw",
  "Slytherin"
]);
 
const prevState = { house: "Gryffindor" };
let nextState = visitNextHogwartsHouse(prevState);
// => { house: "Hufflepuff" }
 
nextState = visitNextHogwartsHouse(nextState);
// => { house: "Ravenclaw" }
 
nextState = visitNextHogwartsHouse(nextState);
// => { house: "Slytherin" }
 
nextState = visitNextHogwartsHouse(nextState);
// => { house: "Gryffindor" }

With single values:

import { cycleState } from "react-state-mutations";
 
const visitNextHogwartsHouse = cycleState([
  "Gryffindor",
  "Hufflepuff",
  "Ravenclaw",
  "Slytherin"
]);
 
const prevState = "Gryffindor";
let nextState = visitNextHogwartsHouse(prevState);
// => "Hufflepuff"
 
nextState = visitNextHogwartsHouse(nextState);
// => "Ravenclaw"
 
nextState = visitNextHogwartsHouse(nextState);
// => "Slytherin"
 
nextState = visitNextHogwartsHouse(nextState);
// => "Gryffindor"

With hooks:

import { useCycle } from "react-state-mutations";
 
const HogwartsHouses = () => {
  const [house, onCycle] = useCycle([
    "Gryffindor",
    "Hufflepuff",
    "Ravenclaw",
    "Slytherin"
  ]);
 
  // sometime later...
  onCycle();
};

With TypeScript, cycle, cycleState, and useCycle all accept an additional type argument for specifying which type the array will hold, as in:

type House = string;
 
cycle<House>("house");

decrement

Decrements a value, as in the example:

import { decrement } from "react-state-mutations";
 
const destroyHorcrux = decrement("horcruxes");
 
const prevState = { horcruxes: 7 };
const nextState = destroyHorcrux(prevState);
// => { count: 6 }

With single values:

import { decrementState } from "react-state-mutations";
 
const prevState = 7;
const nextState = decrementState(prevState);
// => 6

With hooks:

import { useDecrement } from "react-state-mutations";
 
const Horcruxes = () => {
  const [count, onDecrement] = useDecrement(7);
 
  // sometime later...
  onDecrement();
};

With TypeScript, decrement, decrementState, and useDecrement enforce the number type on arguments.

direct

Directly modifies a value. This is mainly valuable when used with combineMutations, as otherwise you could just pass the value to setState as normal. The code below uses combineMutations with others as an example:

import { direct, toggle, combineMutations } from "react-state-mutations";
 
const getCake = direct("cake");
const becomeAWizard = combineMutations(toggle("wizard"), getCake);
 
const prevState = { wizard: false, cake: null };
const nextState = becomeAWizard("chocolate")(prevState);
// => { wizard: true, cake: "chocolate" }

With single values:

import { directState } from "react-state-mutations";
 
const getCake = directState("cake");
 
const prevState = null;
const nextState = getCake(prevState);
// => "cake"

With TypeScript, direct and directState each accept an additional type argument for specifying which type of object will be assigned into the state.

filter

Filters a list, as in the example:

import { filter } from "react-state-mutations";
 
const filterStudents = filter("students");
const findGryffindors = filterStudents(({ house }) => house === "Gryffindor");
 
const prevState = {
  students: [
    { name: "Harry", house: "Gryffindor" },
    { name: "Cedric", house: "Hufflepuff" },
    { name: "Pansy", house: "Slytherin" }
  ]
};
 
const nextState = findGryffindors(prevState);
// => { students: [{ name: "Harry", house: "Gryffindor" }] }

With single values:

import { filterState } from "react-state-mutations";
 
const findGryffindors = filterState(({ house }) => house === "Gryffindor");
 
const prevState = [
  { name: "Harry", house: "Gryffindor" },
  { name: "Cedric", house: "Hufflepuff" },
  { name: "Pansy", house: "Slytherin" }
];
 
const nextState = findGryffindors(prevState);
// => [{ name: "Harry", house: "Gryffindor" }]

With hooks:

import { useFilter } from "react-state-mutations";
 
const Students = () => {
  const [students, onFilter] = useFilter([
    { name: "Harry", house: "Gryffindor" },
    { name: "Cedric", house: "Hufflepuff" },
    { name: "Pansy", house: "Slytherin" }
  ]);
 
  // sometime later...
  onFilter(({ house }) => house === "Gryffindor");
};

With TypeScript, filter, filterState, and useFilter all accept an additional type argument T for specifying which type the array will hold. Additionally the filter function argument is enforced to be of the type ((value: T) => boolean), as in:

interface Student {
  name: string;
  house: string;
}
 
filterState<Student>(({ house }) => house === "Gryffindor");

increment

Increments a value, as in the example:

import { increment } from "react-state-mutations";
 
const upgradeBroom = increment("Nimbus");
 
const prevState = { Nimbus: 2000 };
const nextState = upgradeBroom(prevState);
// => { Nimbus: 2001 }

With single values:

import { incrementState } from "react-state-mutations";
 
const prevState = 2000;
const nextState = incrementState(prevState);
// => 2001

With hooks:

import { useIncrement } from "react-state-mutations";
 
const Nimbus = () => {
  const [version, onIncrement] = useIncrement(2000);
 
  // sometime later...
  onIncrement();
};

With TypeScript, increment, incrementState, and useDecrement enforce the number type on arguments.

map

Maps over a list, as in the example:

import { map } from "react-state-mutations";
 
const mapStudents = map("students");
const graduateStudents = mapStudents(({ year, ...rest }) => ({
  year + 1, ...rest
}));
 
const prevState = {
  students: [
    { name: "Harry", year: 2 },
    { name: "Ginny", year: 1 }
  ]
};
 
const nextState = graduateStudents(prevState);
// => { students: [{ name: "Harry", year: 3 }, { name: "Ginny", year: 2 }] }

With single values:

import { mapState } from "react-state-mutations";
 
const graduateStudents = mapState(({ year, ...rest }) => ({
  year + 1, ...rest
}));
 
const prevState = [
  { name: "Harry", year: 2 },
  { name: "Ginny", year: 1 }
];
 
const nextState = graduateStudents(prevState);
// => [{ name: "Harry", year: 3 }, { name: "Ginny", year: 2 }]

With hooks:

import { useMap } from "react-state-mutations";
 
const Students = () => {
  const [students, onMap] = useMap([
    { name: "Harry", year: 2 },
    { name: "Ginny", year: 1 }
  ]);
 
  // sometime later...
  onMap(({ year, ...rest }) => ({ year + 1, ...rest }));
};

With TypeScript, map, mapState, and useMap all accept an additional type argument T for specifying which type the array will hold. Additionally the map function argument is enforced to be of the type ((value: T) => T), as in:

interface Student {
  name: string;
  year: number;
}
 
mapState<Student>(({ year, ...rest }) => ({ year + 1, ...rest }));

mutate

Mutates a value, as in the example:

import { mutate } from "react-state-mutations";
 
const mutateLupin = mutate("Lupin");
const fullMoon = mutateLupin({ status: "Wolf" });
 
const prevState = { Lupin: { status: "Man", role: "Professor" } };
const nextState = fullMoon(prevState);
// => { Lupin: { status: "Wolf", role: "Professor" } }

With single values:

import { mutateState } from "react-state-mutations";
 
const fullMoon = mutateState({ status: "Wolf" });
 
const prevState = { status: "Man", role: "Professor" };
const nextState = fullMoon(prevState);
// => { status: "Wolf", role: "Professor" }

With TypeScript, the object being used to mutate is enforced to be of type object.

prepend

Prepends a value to a list, as in the example:

import { prepend } from "react-state-mutations";
 
const prependStudent = prepend("students");
 
const prevState = { students: [{ name: "Harry" }, { name: "Hermione" }] };
const nextState = prependStudent({ name: "Ron" })(prevState);
// => { students: [{ name: "Ron" }, { name: "Harry" }, { name: "Hermione" }] }

With single values:

import { prependState } from "react-state-mutations";
 
const prevState = [{ name: "Harry" }, { name: "Hermione" }];
const nextState = prependState({ name: "Ron" })(prevState);
// => [{ name: "Ron" }, { name: "Harry" }, { name: "Hermione" }]

With hooks:

import { usePrepend } from "react-state-mutations";
 
const Students = () => {
  const [students, onPrepend] = usePrepend([
    { name: "Harry" },
    { name: "Hermione" }
  ]);
 
  // sometime later...
  onPrepend({ name: "Ron" });
};

With TypeScript, prepend, prependState, and usePrepend all accept an additional type argument for specifying which type the array will hold, as in:

interface Student {
  name: string;
}
 
prepend<Student>("students");

toggle

Toggles a boolean value, as in the example:

import { toggle } from "react-state-mutations";
 
const toggleWizard = toggle("wizard");
 
const prevState = { wizard: false };
const nextState = toggleWizard(prevState);
// => { wizard: true }

With single values:

import { toggleState } from "react-state-mutations";
 
const prevState = false;
const nextState = toggleState(prevState);
// => true

With hooks:

import { useToggle } from "react-state-mutations";
 
const WizardStatus = () => {
  const [isWizard, onToggle] = useToggle(false);
 
  // sometime later, with Hagrid...
  onToggle();
};

With TypeScript, toggle, toggleState, and useToggle enforce the boolean type on arguments.

Advanced

There are a couple of advanced functions, for creating your own mutations, combining multiple mutations into one function, and creating your own hooks.

makeStandaloneMutation

Creates a mutation that modifies state. Takes as an argument a function that accepts a value and returns the modified value. As in the example:

import { makeStandaloneMutation } from "react-state-mutations";
 
const encrypt = makeStandaloneMutation(value => (
  value.split("").reverse().join("")
));
 
const encryptName = encrypt("name");
 
const prevState = { name: "Harry" };
const nextState = encryptName(prevState);
// => { name: "yrraH" }

With Typescript, makeStandaloneMutation accepts an additional type argument for specifying which type of value will be mutated. For example:

const encrypt = makeStandaloneMutation<string>(value => (
  value.split("").reverse().join("")
));

makeArgumentMutation

Creates a mutation that is a function that takes one argument, that itself returns a function that modifies state. Takes as a function that accepts a value that returns a return that accepts the state and returns the modifies value. As in the example:

import { makeArgumentMutation } from "react-state-mutations";
 
const add = makeArgumentMutation(increment => value => value + increment);
const flyUp100Feet = add("currentHeight")(100);
 
const prevState = { currentHeight: 0 };
const nextState = flyUp100Feet(prevState);
// => { currentHeight: 100 }

With TypeScript, makeArgumentMutation accepts two type arguments, for specifying which type of value will be mutated and for specifying the type of the argument to be passed in. For example:

const add = makeArgumentMutation<number, number>(increment => (
  value => value + increment
));

combineMutations

Combines multiple mutations into a single mutation function. Takes any number of arguments and returns a singular mutation created out of the combination of them all. Can accept either mutations created through react-state-mutations, or plain objects that are meant to be directly setting state.

If any "argument" mutations are passed in, combineMutations will return a function that accepts any number of arguments, that themselves will be passed to the mutations in the order in which they appear in the list given to combineMutations. As in the example:

import { append, increment } from "react-state-mutations";
 
const addToTeam = combineMutations(append("players"), increment("roster"));
 
const prevState = {
  players: [{ name: "Angelina" }, { name: "Alicia" }],
  roster: 2
};
 
const nextState = addToTeam({ name: "Katie" })(prevState);
// => {
//   players: [{ name: "Angelina" }, { name: "Alicia" }, { name: "Katie" }],
//   roster: 3
// };

If all of the mutations that are passed in are "standalone" mutations, then combineMutations will return a function that simply accepts and modifies the state. As in the example:

import { toggle, increment } from "react-state-mutations";
 
const becomeAWizard = combineMutations(toggle("wizard"), increment("wizards"));
 
const prevState = { wizard: false, wizards: 0 };
const nextState = mutation(prevState);
// => { wizard: true, wizards: 1 };

You can additionally pass plain objects into combineMutations that are intended to directly set state. In this case they will be folded into the resultant function and treated as "standalone" mutations that do not accept arguments. As in the example:

import { combineMutations, makeArgumentMutation } from "react-state-mutations";
 
const startFlying = combineMutations(
  makeArgumentMutation(height => value => value + height),
  { flying: true }
);
 
const prevState = { height: 0, flying: false };
const nextState = startFlying(100)(prevState);
// => { height: 100, flying: true };

makeStandaloneHook

Creates a reusable hook based on a mutation that requires no further input. makeStandaloneHook takes two arguments, the first behind the mutation and the second being the default initial value. For example, if you wanted to create a hook that would always multiply the previous value by 2, you could:

import { makeStandaloneHook } from "react-state-mutations";
 
const useDouble = makeStandaloneHook(value => value * 2, 1);

Then, you could use useDouble in your components as any other hooks, as in:

const DoubleDouble = () => {
  const [value, onDouble] = useDouble();
 
  return (
    <button type="button" onClick={onDouble}>
      {value}
    </button>
  );
};

You can also pass a value to useDouble in this example to start at a certain value.

With TypeScript, makeStandaloneHook accepts an additional type argument for specifying which kind of value will be stored in state. For example,

const useDouble = makeStandaloneHook<number>(value => value * 2, 1);

makeArgumentHook

Creates a reusable hook based on a mutation that requires one argument. makeArgumentHook takes two arguments (the same as makeStandaloneHook), the first behind the mutation and the second being the default initial value. For example, if you wanted to create a hook that would count up values in succession, you could:

import { makeArgumentHook } from "react-state-mutations";
 
const useAdder = makeArgumentHook(object => value => value + object, 0);

Then you could use useAdder in your components as any other hooks, as in:

import { useCallback, useState } from "react";
 
const Sum = () => {
  const [number, setNumber] = useState("");
  const onChange = useCallback(event => setNumber(event.target.value), []);
 
  const [value, onAdd] = useAdder();
  const onClick = useCallback(() => onAdd(number), [number]);
 
  return (
    <>
      <input type="number" value={value} onChange={onChange} />
      <button type="button" onClick={onClick}>
        Add
      </button>
    </>
  );
};

With TypeScript, makeArgumentHook accepts two additional type arguments for specifying which kind of value will be stored in state, and which kind of value will be accepted as an argument. For example,

const useAdder = makeArgumentHook<number, number>(
  object => value => value + object, 0
);

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/CultureHQ/react-state-mutations.

License

The code is available as open source under the terms of the MIT License.