unchanged

unchanged

A tiny (~2.0kB minified+gzipped), fast, unopinionated handler for updating JS objects and arrays immutably.

Supports nested key paths via path arrays or dotty syntax, and all methods are curriable (with placeholder support) for composability. Can be a drop-in replacement for the lodash/fp methods get, set, merge, and omit with a 90% smaller footprint.

Table of contents

• Usage
• Types
• Standard methods
  • get
  • getOr
  • set
  • remove
  • has
  • is
  • add
  • merge
  • assign
  • call
• [Transform methods]
  • getWith
  • getWithOr
  • setWith
  • removeWith
  • hasWith
  • isWith
  • addWith
  • mergeWith
  • assignWith
  • callWith
• Additional objects
  • __
• Differences from other libraries
  • lodash
  • ramda
  • Other immutability libraries
• Browser support
• Development

Usage

import {
  __,
  add,
  addWith,
  assign,
  assignWith,
  call,
  callWith,
  get,
  getWith,
  getOr,
  getWithOr,
  has,
  hasWith,
  is,
  isWith,
  merge,
  mergeWith,
  remove,
  removeWith,
  set,
  setWith
} from "unchanged";

const object: unchanged.Unchangeable = {
  foo: "foo",
  bar: [
    {
      baz: "quz"
    }
  ]
};

// handle standard properties
const foo = get("foo", object);

// or nested properties
const baz = set("bar[0].baz", "not quz", object);

// all methods are curriable
const removeBaz = remove("bar[0].baz");
const sansBaz = removeBaz(object);

NOTE: There is no default export, so if you want to import all methods to a single namespace you should use the import * syntax:

import * as uc from "unchanged";

Types

This library is both written in, and provided with, types by TypeScript. The internal types used for specific parameters are scoped to the unchanged namespace.

// the path used to compute nested locations
type Path = (number | string)[] | number | string;
// the callback used in transform methods
type withHandler = (value: any, ...extraParams: any[]) => any;
// the generic object that is computed upon, either an array or object
interface Unchangeable {
  [key: string]: any;
  [index: number]: any;
}

Notice in the Unchangeable interface, there is no reference to symbols. That is because to date, TypeScript does not support Symbols as an index type. If you need to use symbols as object keys, the best workaround I've found is to typecast when it complains:

const symbolKey: string = (Symbol("key") as unknown) as string;

const object: { [symbolKey]: string } = {
  [symbolKey]: "bar"
};

If there is a better alternative for having dynamic Symbol indices, let me know! Happy to accept any PRs from those more experienced in TypeScript than myself.

Standard methods

get

function get(path: unchanged.Path, object: unchanged.Unchangeable): any;

Get the value at the path requested on the object passed.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(get("foo[0].bar", object)); // baz
console.log(get(["foo", 0, "bar"], object)); // baz

getOr

function getOr(
  fallbackValue: any,
  path: unchanged.Path,
  object: unchanged.Unchangeable
): any;

Get the value at the path requested on the object passed, with a fallback value if that path does not exist.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(getOr("blah", "foo[0].bar", object)); // baz
console.log(getOr("blah", ["foo", 0, "bar"], object)); // baz
console.log(getOr("blah", "foo[0].nonexistent", object)); // blah

set

function set(
  path: unchanged.Path,
  value: any,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the value assigned to the final key on the path specified.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(set("foo[0].bar", "quz", object)); // {foo: [{bar: 'quz'}]}
console.log(set(["foo", 0, "bar"], "quz", object)); // {foo: [{bar: 'quz'}]}

remove

function remove(
  path: unchanged.Path,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the final key on the path removed if it exists.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(remove("foo[0].bar", object)); // {foo: [{}]}
console.log(remove(["foo", 0, "bar"], object)); // {foo: [{}]}

has

function has(path: unchanged.Path, object: unchanged.Unchangeable): boolean;

Returns true if the object has the path provided, false otherwise.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(has("foo[0].bar", object)); // true
console.log(has(["foo", 0, "bar"], object)); // true
console.log(has("bar", object)); // false

is

function is(
  path: unchanged.Path,
  value: any,
  object: unchanged.Unchangeable
): boolean;

Returns true if the value at the path in object is equal to value based on SameValueZero equality.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};

console.log(is("foo[0].bar", "baz", object)); // true
console.log(is(["foo", 0, "bar"], "baz", object)); // true
console.log(is("foo[0].bar", "quz', object)); // false

add

function add(
  path: unchanged.Path,
  value: any,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the value added at the path specified. This can have different behavior depending on whether the item is an object or an array; objects will simply add / set the key provided, whereas arrays will add a new value to the end.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: 'baz'
    }
  ]
};

// object
console.log(add('foo', 'added value' object)); // {foo: [{bar: 'baz'}, 'added value']}
console.log(add(['foo'], 'added value', object)); // {foo: [{bar: 'baz'}, 'added value']}

// array
console.log(add('foo[0].quz', 'added value' object)); // {foo: [{bar: 'baz', quz: 'added value'}]}
console.log(add(['foo', 0, 'quz'], 'added value', object)); // {foo: [{bar: 'baz', quz: 'added value'}]}

Notice that the Object usage is idential to the set method, where a key needs to be specified for assignment. In the case of an Array, however, the value is pushed to the array at that key.

NOTE: If you want to add an item to a top-level array, pass null as the key:

const object = ["foo"];

console.log(add(null, "bar", object)); // ['foo', 'bar']

merge

function merge(
  path: unchanged.Path,
  value: unchanged.Unchangeable,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object that is a deep merge of value into object at the path specified. If you want to perform a shallow merge, see assign.

const object1: unchanged.Unchangeable = {
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  }
};
const object2: unchanged.Unchangeable = {
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
};

console.log(merge("baz", object2, object1));
/*
{
  foo: 'bar',
  baz: {
    one: 'new value',
    deeply: {
      nested: 'other value',
      untouched: true,
    },
    two: 'value2',
    three: 'value3
  }
}

NOTE: If you want to merge the entirety of both objects, pass null as the key:

console.log(merge(null, object2, object1));
/*
{
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  },
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
}
*/

assign

function assign(
  path: unchanged.Path,
  value: unchanged.Unchangeable,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object that is a shallow merge of value into object at the path specified. If you want to perform a deep merge, see merge.

const object1: unchanged.Unchangeable = {
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  }
};
const object2: unchanged.Unchangeable = {
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
};

console.log(assign("baz", object2, object1));
/*
{
  foo: 'bar',
  baz: {
    one: 'new value',
    deeply: {
      nested: 'other value',
    },
    two: 'value2',
    three: 'value3
  }
}

NOTE: If you want to assign the entirety of both objects, pass null as the key:

console.log(assign(null, object2, object1));
/*
{
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  },
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
}
*/

call

function call(
  path: unchanged.Path,
  parameters: any[],
  object: unchanged.Unchangeable,
  context?: any = object
): any;

Call the method at the path requested on the object passed, and return what it's call returns.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar(a, b) {
        return a + b;
      }
    }
  ]
};

console.log(call("foo[0].bar", [1, 2], object)); // 3
console.log(call(["foo", 0, "bar"], [1, 2], object)); // 3

You can also provide an optional fourth parameter of context, which will be the this value in the method call. This will default to the object itself.

const object: unchanged.Unchangeable = {
  calculate: true,
  foo: [
    {
      bar(a, b) {
        return this.calculate ? a + b : 0;
      }
    }
  ]
};

console.log(call("foo[0].bar", [1, 2], object)); // 3
console.log(call("foo[0].bar", [1, 2], object, {})); // 0

NOTE: Because context is optional, it cannot be independently curried; you must apply it in the call when the object is passed.

Transform methods

Each standard method has it's own related With method, which accepts a callback fn as the first curried parameter. In most cases this callback serves as a transformer for the value retrieved, set, merged, etc.; the exception is removeWith, where the callback serves as a validator as to whether to remove or not.

The signature of all callbacks is the withHandler specified in Types. Because extraParams are optional parameters, they cannot be independently curried; you must apply them in the call when the object is passed.

getWith

function getWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable,
  ...extraParams?: any[]
): any;

Get the return value of fn based on the value at the path requested on the object passed. fn is called with the current value at the path as the first parameter, and any additional parameters passed as extraParams following that.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (value: any, nullValue: any): any =>
  currentValue === nullValue ? null : currentValue;

console.log(getWith(fn, "foo[0].bar", object)); // 'baz'
console.log(getWith(fn, "foo[0].bar", object, "baz")); // null
console.log(getWith(fn, ["foo", 0, "bar"], object)); // 'baz'
console.log(getWith(fn, ["foo", 0, "bar"], object, "baz")); // null

getWithOr

function getWithOr(
  fn: unchanged.withHandler,
  fallbackValue: any,
  path: unchanged.Path,
  object: unchanged.Unchangeable,
  ...extraParams?: any[]
): any;

Get the return value of fn based on the value at the path requested on the object passed, falling back to fallbackValue when no match is found at path. When a match is found, fn is called with the current value at the path as the first parameter, and any additional parameters passed as extraParams following that.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (value: any, nullValue: any): any =>
  currentValue === nullValue ? null : currentValue;

console.log(getWithOr(fn, "quz", "foo[0].bar", object)); // 'baz'
console.log(getWithOr(fn, "quz", "foo[0].bar", object, "baz")); // null
console.log(getWithOr(fn, "quz", "foo[0].notFound", object, "baz")); // 'quz'
console.log(getWithOr(fn, "quz", ["foo", 0, "bar"], object)); // 'baz'
console.log(getWithOr(fn, "quz", ["foo", 0, "bar"], object, "baz")); // null
console.log(getWithOr(fn, "quz", ["foo", 0, "notFound"], object, "baz")); // 'quz'

setWith

function setWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable,
  ...extraParams?: any[]
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the return value of fn assigned to the final key on the path specified. fn is called with the current value at the path as the first parameter, and any additional parameters passed as extraParams following that.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (value: any, preventUpdate: boolean): any =>
  preventUpdate ? currentValue : "quz";

console.log(setWith(fn, "foo[0].bar", object)); // {foo: [{bar: 'quz'}]}
console.log(setWith(fn, "foo[0].bar", object, true)); // {foo: [{bar: 'baz'}]}
console.log(setWith(fn, ["foo", 0, "bar"], object)); // {foo: [{bar: 'quz'}]}
console.log(setWith(fn, ["foo", 0, "bar"], object, true)); // {foo: [{bar: 'baz'}]}

removeWith

function removeWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable,
  ...extraParams?: any[]
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the final key on the path removed if it exists and the return from fn is truthy.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (
  value: any,
  shouldNotRemove: boolean
): boolean => !shouldNotRemove && value === "baz";

console.log(removeWith(fn, "foo[0].bar", object)); // {foo: [{}]}
console.log(removeWith(fn, "foo[0].bar", object, true)); // {foo: [{bar: 'baz'}]}
console.log(removeWith([fn, "foo", 0, "bar"], object)); // {foo: [{}]}
console.log(removeWith([fn, "foo", 0, "bar"], object, true)); // {foo: [{bar: 'baz'}]}

hasWith

function hasWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable,
  ...extraParams?: any[]
): boolean;

Returns true if the return value of fn based on the value returned from path in the object returns truthy, false otherwise.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (
  value: any,
  shouldBeNull: boolean
): boolean => (shouldBeNull ? value === null : value === "baz");

console.log(hasWith(fn, "foo[0].bar", object)); // true
console.log(hasWith(fn, "foo[0].bar", object, true)); // false
console.log(hasWith(fn, ["foo", 0, "bar"], object)); // true
console.log(hasWith(fn, ["foo", 0, "bar"], object, true)); // false
console.log(hasWith(fn, "bar", object)); // false

isWith

function isWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable
): boolean;

Returns true if the return value of fn based on the value returned from path in the object is equal to value based on SameValueZero equality.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz",
      quz: "not baz"
    }
  ]
};
const fn: unchanged.withHandler = (value: any): number =>
  value && value.length === 3;

console.log(isWith(fn, "foo[0].bar", object)); // true
console.log(isWith(fn, ["foo", 0, "bar"], object)); // true
console.log(isWith(fn, "foo[0].quz", object)); // false

addWith

function addWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object based on the object passed, with the return value of fn added at the path specified. This can have different behavior depending on whether the item is an object or an array; objects will simply add / set the key provided, whereas arrays will add a new value to the end.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar: "baz"
    }
  ]
};
const fn: unchanged.withHandler = (value: any) =>
  value
    ? value
        .split("")
        .reverse()
        .join("")
    : "new value";

// object
console.log(addWith(fn, "foo", object)); // {foo: [{bar: 'baz'}, 'new value']}
console.log(addWith(fn, ["foo"], object)); // {foo: [{bar: 'baz'}, 'new value']}

// array
console.log(addWith(fn, "foo[0].bar", object)); // {foo: [{bar: 'zab'}]}
console.log(addWith(fn, ["foo", 0, "bar"], object)); // {foo: [{bar: 'zab''}]}

mergeWith

function mergeWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object that is a deep merge of the return value of fn into object at the path specified if a valid mergeable object, else returns the original object. If you want to perform a shallow merge, see assignWith.

const object1: unchanged.Unchangeable = {
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  }
};
const object2: unchanged.Unchangeable = {
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
};
const fn: unchanged.withHandler = (value: any) =>
  value && value.one === "value1" ? object2 : null;

console.log(mergeWith(fn, "baz", object1));
/*
{
  foo: 'bar',
  baz: {
    one: 'new value',
    deeply: {
      nested: 'other value',
      untouched: true,
    },
    two: 'value2',
    three: 'value3
  }
}
*/
console.log(mergeWith(fn, "baz.deeply", object1));
/*
// untouched object1
{
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: 'value',
      untouched: true,
    },
    two: "value2"
  }
}
*/

NOTE: If you want to merge the entirety of both objects, pass null as the key:

console.log(mergeWith(fn, null, object1));
/*
{
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  },
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
}
*/

assignWith

function assignWith(
  fn: unchanged.withHandler,
  path: unchanged.Path,
  object: unchanged.Unchangeable
): unchanged.Unchangeable;

Returns a new object that is a shallow merge of the return value of fn into object at the path specified if a valid mergeable object, else returns the original object. If you want to perform a deep merge, see mergeWith.

const object1: unchanged.Unchangeable = {
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: "value",
      untouched: true
    },
    two: "value2"
  }
};
const object2: unchanged.Unchangeable = {
  one: "new value",
  deeply: {
    nested: "other value"
  },
  three: "value3"
};
const fn: unchanged.withHandler = (value: any) =>
  value && value.one === "value1" ? object2 : null;

console.log(assignWith(fn, "baz", object1));
/*
{
  foo: 'bar',
  baz: {
    one: 'new value',
    deeply: {
      nested: 'other value',
    },
    two: 'value2',
    three: 'value3
  }
}
*/
console.log(assignWith(fn, "baz.deeply", object1));
/*
// untouched object1
{
  foo: "bar",
  baz: {
    one: "value1",
    deeply: {
      nested: 'value',
      untouched: true,
    },
    two: "value2"
  }
}
*/

callWith

function callWith(
  path: unchanged.Path,
  parameters: any[],
  object: unchanged.Unchangeable,
  context?: any = object
): any;

Call the method returned from fn based on the path specified on the object, and if a function return what it's call returns.

const object: unchanged.Unchangeable = {
  foo: [
    {
      bar(a, b) {
        return a + b;
      }
    }
  ]
};
const fn: unchanged.withHandler = (value: any): any =>
  typeof value === fn
    ? fn
    : () =>
        console.error("Error: Requested call of a method that does not exist.");

console.log(callWith(fn, "foo[0].bar", [1, 2], object)); // 3
console.log(callWith(fn, ["foo", 0, "bar"], [1, 2], object)); // 3
callWith(fn, "foo[1].nope", object); // Error: Requested call of a method that does not exist.

You can also provide an optional fourth parameter of context, which will be the this value in the method call. This will default to the object itself.

const object: unchanged.Unchangeable = {
  calculate: true,
  foo: [
    {
      bar(a, b) {
        return this.calculate ? a + b : 0;
      }
    }
  ]
};
const fn: unchanged.withHandler = (value: any): any =>
  typeof value === fn
    ? fn
    : () =>
        console.error("Error: Requested call of a method that does not exist.");

console.log(callWith(fn, "foo[0].bar", [1, 2], object)); // 3
console.log(callWith(fn, "foo[0].bar", [1, 2], object, {})); // 0

NOTE: Because context is optional, it cannot be independently curried; you must apply it in the call when the object is passed.

Additional objects

__

A placeholder value used to identify "gaps" in a curried function, allowing for earlier application of arguments later in the argument order.

import {__, set} from 'unchanged';

const thing = {
  foo: 'foo';
};

const setFoo = set('foo', __, thing);

setFooOnThing('bar');

Differences from other libraries

lodash

lodash/fp (the functional programming implementation of lodash) is identical in implementation to unchanged's methods, just with a 10.5x larger footprint. These methods should map directly:

• lodash => unchanged
• curry.placeholder => __
• get => get
• getOr => getOr
• merge => merge
• omit => remove
• set => set

ramda

ramda is similar in its implementation, however the first big difference is that dot-bracket syntax is not supported by ramda, only path arrays. The related methods are:

• ramda => unchanged
• __ => __
• path => get
• pathOr => getOr
• merge => merge
• omit => remove
• assocPath => set

Another difference is that the ramda methods that clone objects (assocPath, for example) only work with objects; arrays are implicitly converted into objects, which can make updating collections challenging.

The last main difference is the way that objects are copied, example:

function Foo(value) {
  this.value = value;
}

Foo.prototype.getValue = function() {
  return this.value;
};

const foo = new Foo("foo");

// in ramda, both own properties and prototypical methods are copied to the new object as own properties
const ramdaResult = assoc("bar", "baz", foo);

console.log(ramdaResult); // {value: 'foo', bar: 'baz', getValue: function getValue() { return this.value; }}
console.log(ramdaResult instanceof Foo); // false

// in unchanged, the prototype of the original object is maintained, and only own properties are copied as own properties
const unchangedResult = set("bar", "baz", foo);

console.log(unchangedResult); // {value: 'foo', bar: 'baz'}
console.log(unchangedResult instanceof Foo); // true

This can make ramda more performant in certain scenarios, but at the cost of having potentially unexpected behavior.

Other immutability libraries

This includes popular solutions like Immutable.js, seamless-immutable, mori, etc. These solutions all work well, but with one caveat: you need to buy completely into their system. Each of these libraries redefines how the objects are stored internally, and require that you learn a new, highly specific API to use these custom objects. unchanged is unopinionated, accepting standard JS objects and returning standard JS objects, no transformation or learning curve required.

Browser support

• Chrome (all versions)
• Firefox (all versions)
• Edge (all versions)
• Opera 15+
• IE 9+
• Safari 6+
• iOS 8+
• Android 4+

Development

Standard stuff, clone the repo and npm install dependencies. The npm scripts available:

• benchmark => run benchmark suite comparing top-level and deeply-nested get and set operations with lodash and ramda
• build => run rollup to build dist files for CommonJS, ESM, and UMD consumers
• clean => run rimraf on the dist folder
• dev => run webpack dev server to run example app / playground
• dist => runs clean and build
• lint => run ESLint against all files in the src folder
• lint:fix => run lint with autofixing applied
• prepublish => runs prepublish:compile when publishing
• prepublish:compile => run lint, test:coverage, dist
• test => run AVA test functions with NODE_ENV=test
• test:coverage => run test but with nyc for coverage checker
• test:watch => run test, but with persistent watcher

Changelog

2.0.0

Rewrite in TypeScript!

BREAKING CHANGES

• transform has changed to be setWith, and the signature has changed as well (see the documentation for details)

NEW FEATURES

• Added is method for assertion
• Added function-first *With methods corresponding to each existing method (see the documentation for details)
• TypeScript typings

ADDITIONAL CHANGES

• Faster gets, sets, merges, and removes
• Distinct main, module, and browser builds for better universality of consumption