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feat: enforce global singleton for all exposed modules via module federation #308

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feat: enforce global singleton for all exposed modules via module federation #308

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28 changes: 18 additions & 10 deletions src/virtualModules/virtualExposes.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4,23 +4,31 @@ export const VIRTUAL_EXPOSES = 'virtual:mf-exposes';
export function generateExposes() {
const options = getNormalizeModuleFederationOptions();
return `
const GLOBAL_KEY = '__MF_SINGLETONS__';
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should not add more globals, this entire thing already exists in FEDERATION
should be using loadShare('lib', {from: 'name of current app'}); or at least from share_scope_map off federation

This will also not work with module layers which is being introduced, where you can have concurrent parallel share scopes who still respect singletons, but within the scope - so in cases like next, i have 13 singletons for react.

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According to the tests I have made, the instance is not unique, so the instance may be recreated. I'd like to know what your approach is to avoid the problem of multiple instances

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There should be 1 instance per app. Recreation of instances shouldn't happen.
If thats is happening theres a bigger problem

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instance is stored in memory / state and registered in the federation global, we search for the instance by name.

These arch specs may be useful. https://github.com/module-federation/core/pull/3955/files#diff-5596198c9d0ae99e768d378410829b221f2ac61b098aa86e5c55a994d6efb964

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This may be the case for Webpack, but not for Vite. Based on my tests, I created an Axios instance with Keycloak for the token part and shared this instance with the other remotes. However, doing so resulted in the instances being created twice.

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yeah then its a bug in vite implementation. all webpack does is implement the runtime package.

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@gioboa what do you think?

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I can totally trust @ScriptedAlchemy

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@aachik-trimoz aachik-trimoz Aug 4, 2025 •
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@gioboa do you think you can do an investigation to know why we don't have this in the Vite version

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Id check why instances are recreated. In webpack. We do have 1 aspect where we assign the instance associated with that runtime to webpack_require. So we can access the instance throughout the application.
However I can also call init() multiple times over and it doesn't recreate the instance because we store it in a scoped variable - but thats what /runtime init does.
We did introduce createInstance now as well to runtime.

const globalObj = typeof globalThis !== 'undefined' ? globalThis : window;
globalObj[GLOBAL_KEY] = globalObj[GLOBAL_KEY] || {};

export default {
${Object.keys(options.exposes)
.map((key) => {
const singletonKey = JSON.stringify(key);
return `
${JSON.stringify(key)}: async () => {
const importModule = await import(${JSON.stringify(options.exposes[key].import)})
const exportModule = {}
Object.assign(exportModule, importModule)
Object.defineProperty(exportModule, "__esModule", {
value: true,
enumerable: false
})
return exportModule
${singletonKey}: async () => {
if (!globalObj[GLOBAL_KEY][${singletonKey}]) {
const importModule = await import(${JSON.stringify(options.exposes[key].import)});
const exportModule = {};
Object.assign(exportModule, importModule);
Object.defineProperty(exportModule, "__esModule", {
value: true,
enumerable: false
});
globalObj[GLOBAL_KEY][${singletonKey}] = exportModule;
}
return globalObj[GLOBAL_KEY][${singletonKey}];
}
`;
})
.join(',')}
}
}
`;
}