0.1.3 • Public • Published

Make plain json data(array and object) immutable

It's using Object.freeze() and Object.defineProperty() to achieve immutability. See compatible on compat-table(shortly IE9+).
Should only work for json data, not function, date and other user-defined/third-party-defined object. In short, it could be the replacement of array([]) and plain object({}).


import immutable from 'plain-immutable';

const arr = immutable([1, 2, { a: 'b' }]);
arr[0] = -1; // it will throw
arr[2].a = 'c'; // it will throw too even you want to change the nested object

console.log(arr[2].a);// b
console.log(JSON.stringify(arr));// [1,2,{"a":"b"}]

const mArr = arr.set(0, -1);
console.log(arr[0]);// 1
console.log(mArr[0]);// -1

Static Methods


Alias immutable.fromJSON(), immutable.fromJS()
Make the value immutable, only for array and plain object. If you pass a literal value(string, number or boolean) or other types, It will do nothing and return itself. The value will be deeply made immutable, no copy.

import immutable from 'plain-immutable';

const arr = [{ a: 1 }];
const arr1 = immutable(arr);
console.log(arr === arr1);// true

isImmutable(value: any)

Alias immutable.isImmutable()
True if the value is an immutable array or object.

import immutable, {isImmutable} from 'plain-immutable';

console.log(immutable.isImmutable(1)); // false
console.log(isImmutable(1)); // false
console.log(isImmutable(true)); // false
console.log(isImmutable('a')); // false
console.log(isImmutable({})); // false
console.log(isImmutable([])); // false
console.log(isImmutable(Object.create(null))); // false
console.log(isImmutable(immutable({}))); // true
console.log(isImmutable(immutable([]))); // true
console.log(isImmutable(immutable(Object.create(null)))); // true

Additional Instace Methods

These methods are applied to both immutable object and immutable array. So make sure that your object don't have these properties.

.set(key: string, value: json|function)

Same like .setIn(key, value), but only allow string type key

.setIn(keyPath: string|array, value: json|function)

Return a new immutable copy having set the value at leaf key of key path. If any key in the path is not existent, create a plain object at that key. You can pass a function(setter) which will be used to generate new value at the leaf key.

const obj = immutable({ a: 1, nums: [] });
const obj1 = obj.set('a', 2); // {a: 2, nums: []}
const obj2 = obj.setIn(['nums'], nums => nums.push(1)); // {a: 1, nums: [1]}

.remove(key: string)

Alias .delete()
Same like .removeIn(key), but only allow string type key

.removeIn(keyPath: string|array)

Alias .deleteIn()
Return a new immutable copy having removed the value at leaf key of key path. If any key in the path is not existent, nothing will be changed.

const obj = immutable({ a: 1, nums: [1] });
const obj1 = obj.remove('a'); // {nums: [1]}
const obj2 = obj.removeIn(['nums', 0]); // {a: 1, nums: []}

.merge(strategy?: boolean|function, value: json)

Return a new immutable copy having merged with the value by the strategy. Strategy is used to deal conflicts(same key but different values). There are three types of strategy:

  • false(or not specified): Old value will be overwriten
  • true: Deeply merge if the two values are with same type(array or object)
  • function: Called a merger with (prev, next, key)=>any. It will be invoked on each conflicted key.
const arr = immutable([1, { a: 2, b: 3 }]);
console.log(arr.merge([-1, { c: 4 }])); // [-1, {c: 4}]
console.log(arr.merge(true, [-1, { c: 4 }])); // [-1, {a: 2, b: 3, c: 4}]

console.log(immutable([1, 2]).merge((p, n) => p + n, [2, 3])); // [3, 5]


Alias .asMutable()
Return a mutable copy. That is to say the return value is normal plain object or array. You can use =(assign operator) to set new key or value, and all methods will be restored to original behavior(like arr.push() will return new length other than new immutable array).
You should know that .mutable() will not make nested object(array) mutable.

const arr = immutable([1, 2, 3]);
const arr1 = arr.mutable();
arr1[0] = -1;
console.log(arr1); // [-1, 2, 3]


Since array has a lot of methods like push and slice. Some are mutation operations while some are not.
For non-mutation methods that doesn't surely return literal value like slice, they are replaced to return immutable value. These methods are slice, concat, map, reduce, reduceRight, filter.
For mutation methods like push, they are replaced to return a new immutable copy other than their orignal returns. These methods are push, pop, shift, unshift, fill, sort, splice, reverse, copyWithin.
If any of these methods doesn't exist, no replacement for that method exists too.

const arr = immutable([1, 2, 3]);
const newArr = arr.push(4); // [1, 2, 3, 4]


Licensed under MIT

Copyright (c) 2017 Tian Jian

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