Just some super basic usage, getting an error saying that dequal isn't a function since the update to 2.0

import dequal from 'dequal'

function useDeepCompareMemoize(value) {
  const ref = React.useRef()

  if (!dequal(value, ref.current)) {
    ref.current = value
  }

  return ref.current
}

In tsc nightly a new module resolutions scheme is introduced called node12 or nodenext which uses this "exports" field in package.json files. When this is present and being used then the old root "types" is not used. You have to specify the types in the specific exports (when the files are not adjacent).

Here is the code to support Map and Set conventionalized for older browsers (which may not be necessary depending on what you are doing for transpile). I have this locally along with unit test additions. I can do a pull request, you can add to your code, or (of course) you can ignore:

if(typeof(Map)==="function" && ctor === Map) {
			if(foo.size === bar.size) {
				for(const [key,value] of foo.entries()) { // Maps are mathematically unordered
					if(!dequal(bar.get(key),value)) { // so ... simple existence of same key value is good enough
						return false;
					}
				}
				return true;
			}
			return false;
		}
		
		if(typeof(Set)==="function" && ctor === Set) {
			if(foo.size === bar.size) {
				for(const fvalue of foo.entries()) { // Sets are mathematically unordered
					let found;
					for(const bvalue of bar.entries()) { // so ... need to compare each entry
						if(found = dequal(fvalue,bvalue)) {
							break;
						}
					}
					if(!found) {
						return false;
					}
				}
				return true;
			}
			return false;
		}

Hi!

I just noticed this library does not compare Sets correctly.

Repro:

var dequal = require("dequal")

let a = new Set([1,2,3,4])
let b = new Set([1,2,3,4])

console.log(dequal(a,b))

https://runkit.com/embed/yiu9lr2kont0

As an example, lodash's isEqual does compare Sets and in the above use case does return true.

This is also related to https://github.com/kentcdodds/use-deep-compare-effect/issues/15

Fran

Great library, thanks ! 👍

One small suggestion -- it's be nice if we could select between "loose" or "strict" equality checking. Currently, dequal(1, true) returns false, which is correct if we're checking 1 === true, but not for 1 == true. Similar for dequal(null, undefined).

Any chance of making the type of equality check configurable?

There may be cases when your Array comparison breaks. Although not necessarily a good coding approach, sometimes non-numeric values are added to Arrays by programmers for book-keeping (The "arrays" in the DOM, e.g. attributes, are kind of like this). If you simply delete the Array section of your code, the unit tests still pass since arrays are just regular objects that only have numeric keys by default plus a length property and some extra functions. Also your code will be slightly smaller while also addressing this edge case.

Thanks for the great projejct @lukeed! Discovered this while porting a project of mine from tape to uvu (this was the only blocker):

class Foo {}

const a = new Foo();
const b = new Foo();

dequal(a, b); // false :(

I guess this would be fixed by replacing the ctor === Object check with typeof foo === 'object'. Was this an issue with performance? Comparing class instances and other non-basic objects is indispensable when writing unit tests.

Related: #2

Although bundt is a devDependency it does not run on Debian after a regular npm install. Should it?

npm run bundt
npm ERR! missing script: bundt

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/syblackwell/.npm/_logs/2020-07-17T23_56_51_497Z-debug.log

ls node_modules
buffer-from  dequal  kleur    rewrite-imports  source-map-support  uvu
bundt        diff    mk-dirs  sade             terser
commander    esm     mri      source-map       totalist

I tried to use dequal as lodash.isEqual replacement, but find out that when comparing two Invalid Dates dequal returns true.

Not sure if this is correct, because of possible false possitives - new Date('foo') is not same as new Date('bar'). Solution - instead of comparing date.getTime(), isNaN(date) should be considered.

Again, not sure what result to expect here plus changing this will cause BREAKING-CHANGE.

I'll stick with lodash's isEqual for now :(

I tried to use dequal as lodash.isEqual replacement, but find out that when comparing two Invalid Dates dequal returns true.

Not sure if this is correct, because of possible false possitives - new Date('foo') is not same as new Date('bar'). Solution - instead of comparing date.getTime(), isNaN(date) should be considered.

Again, not sure what result to expect here plus changing this will cause BREAKING-CHANGE.

I'll stick with lodash's isEqual for now :(

Module declaration did not work because index.d.ts is not a rootType, so I created a declaration file for each mode.

Same as https://github.com/lukeed/klona/pull/22

See https://stackblitz.com/edit/js-gxcyih?file=index.js

I think it's because of the way we fall into the "plain" object comparison in https://github.com/lukeed/dequal/blob/master/src/index.js#L73-L80

const x = new URLSearchParams();
x.append("foo", "bar");

for (i in x) {
  if (x.hasOwnProperty(i)) console.info(i);
}

=> Nothing gets printed because e.g. entries is always the same, but the stuff returned from entries is not.

Reverse iteration over TypedArrays was starting at foo.byteLength - 1, not foo.length - 1. For TypedArrays with .BYTES_PER_ELEMENT greater than 1, that was resulting in up to 7*foo.length needless pairs of out-of-bounds array accesses and undefined === undefined comparisons.

If both arguments have cycles, like if you're trying to compare doubly-linked lists, dequal goes into an infinite loop.

repro:

const a: any = {}, b: any = {};
a.next = b;
b.previous = a;

const c: any = {}, d: any = {};
c.next = d;
d.previous = c;

dequal(a, c);

This is definitely an edge-case, but when comparing objects like Array across iframe boundaries, instanceof will not work. See MDN's example of this: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray#instanceof_vs_isArray