TypeError: equal is not a function in maskFragment.js with @wry/equality 0.5.7

[alexanderoskin]

Issue Description

Current Behavior

Getting TypeError: equal is not a function error when using Apollo Client 4.0.3 with @wry/equality version 0.5.7 during SSR (Server-Side Rendering).

Error Stack Trace

TypeError: equal is not a function
    at maskFragment (file:///path/to/node_modules/@apollo/client/masking/maskFragment.js:23:9)
    at QueryManager.maskFragment (file:///path/to/node_modules/@apollo/client/core/QueryManager.js:948:13)
    at file:///path/to/node_modules/@apollo/client/react/hooks/useFragment.js:54:48
    at Object.useMemo (/path/to/node_modules/react-dom/cjs/react-dom-server.node.development.js:3903:20)
    at process.env.NODE_ENV.exports.useMemo (/path/to/node_modules/react/cjs/react.development.js:1209:34)
    at useFragment_ (file:///path/to/node_modules/@apollo/client/react/hooks/useFragment.js:33:24)
    at useFragment (file:///path/to/node_modules/@apollo/client/react/hooks/useFragment.js:17:51)

Root Cause Analysis

The issue is in /masking/maskFragment.js which uses:

import equal from "@wry/equality";

However, @wry/equality 0.5.7 has a build bug where the ESM version (lib/index.js) is missing the default export:

ESM version (lib/index.js) - BROKEN:

export function equal(a, b) { ... }
// Missing: export default equal;

CommonJS version (lib/bundle.cjs) - WORKS:

exports.equal = equal;
exports.default = equal;  // ← This exists

Workaround

Temporarily fix by changing the import in maskFragment.js:

// Change from:
import equal from "@wry/equality";

// To:
import { equal } from "@wry/equality";

Link to Reproduction

https://

Reproduction Steps

1. Install Apollo Client 4.0.3
2. Use useFragment hook in SSR context with ESM modules
3. Error occurs because import equal from "@wry/equality" returns undefined in ESM

@apollo/client version

4.0.3

[phryneas]

Hi @alexanderoskin,
thank you for the report!

Generally - I believe that default export is there, it's here on line 16: https://app.unpkg.com/@wry/equality@0.5.7/files/lib/index.js#L16

That said, we've been mixing both import styles and probably need to get that cleaned up anyways.

I've opened a PR to fix this: #12900 - this should go out in our next patch release.

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