atlas-deep-equals

atlas-deep-equals

Recursively tests deep or shallow equality for primitive structures.

install

npm install --save atlas-deep-equals

why

This is a very fast, key-order independent, deep/shallow equality check for simple data trees. This is meant for comparing simple (plain old javascript objects) data and is not to be used on objects containing complex prototype chains.

JSON.stringify(a) === JSON.stringify(b) is an unsafe way to deep-compare objects, and is not used here. Exceptions for Date, Regexp and NaN objects are outside the scope of this package.

examples

First, import the equals function:

const equals = require("atlas-deep-equals");

shallow comparisons

If you know your data is not nested or you are using immutable subtrees, simply perform a shallow equals:

const props1 = {color: "red", name: "atlas", id: "ABhGjUyFt", age: 109}
const props2 = {color: "red", name: "atlas", id: "ABhGjUyFt", age: 29}

equals(props1, props2)
// false

deep comparisons

If you have nested data and are not using immutability, then you can pass true as a third argument to perform a recursive comparison:

const props1 = {
  posts: [
    {id: 1, text: "Hi!"},
    {id: 2, text: "Hello."},
    {id: 3, text: "Hola!!"}
  ],
  comments: [
    {id: 4, text: "Bye"},
    {id: 5, text: "see you later"}
  ]
}
const props2 = {
  posts: [
    {id: 1, text: "Hi!"},
    {id: 2, text: "Hello."},
    {id: 3, text: "Hola!!"}
  ],
  comments: [
    {id: 4, text: "Bye"},
    {id: 5, text: "see you later"}
  ]
}
const isDeep = true;
equals(props1, props2, isDeep);
// true

immutability

Immutable objects make use of strict reference equality (===) to perform fast comparisons regardless of how nested the data is. Every time an immutable object receives an update, a brand new reference will be returned that points to the new version of the object.

Both shallow and deep equals will perform a reference equality check (===) as a short circuit before checking anything else. In the event that the references are different, equals will iterate (and recurse, if deep) over the object's keys/indices.

This means that if props1 and props2 are themselves immutable, do not use equals. Instead, use props1 === props2 to check if they are not equal to each other.

Similarly, if props1 and props2 are mutable, but their top-level fields are all primitives and/or immutable, do not use deep equals. Insead, use equals(props1, props2) to perform a fast shallow comparison.

caveats

Date and RegExp

Deep-equality libraries tend to make exceptions for commonly used objects:

...
if (isDate(a)) return isDate(b) && a.valueOf() === b.valueOf();
if (isRegExp(a)) return isRegExp(b) && a.toString() === b.toString();
...

This library doesn't. If a complex type can be reduced to a primitive, it makes more sense for the caller to normalize the input than for equals to guess what non-primitives the caller is using.

NaN

NaN usually arises in javascript because of an error in some logic -- equals assumes NaN is taken care of by the caller. Testing for NaN in equals would be trivial, but seems unnecessary; I may decide to add a NaN check later, though.

plain old javascript objects

Unless you are using some sort of immutable object (making deep equals irrelevant), equals expects simple object and array literals, and primitive types. Using complicated types like Date and MyClass may not result in expected behavior.