Fix LocalStorageAssignmentShim reading localStorage["undefined"] during construction#278
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bertilhatt merged 3 commits intomainfrom Mar 27, 2026
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…ng construction
Class field initializers for `size` and `[Symbol.toStringTag]` called
`this.getCache()` before the constructor body assigned `this.localStorageKey`,
causing `localStorage.getItem("undefined")`. If that key held non-JSON data,
`JSON.parse` threw and the SDK failed to initialize.
Convert both to getters so they no longer eagerly read localStorage during
construction. This also fixes a secondary bug where `size` was a stale
snapshot that never updated after mutations.
FFESUPPORT-610
Made-with: Cursor
dd-oleksii
approved these changes
Mar 26, 2026
2 tasks
Co-authored-by: Oleksii Shmalko <oleksii.shmalko@datadoghq.com>
Remove the explicit `string` type annotation from `[Symbol.toStringTag]` to satisfy `@typescript-eslint/no-inferrable-types` while keeping the reviewed field-style implementation. Made-with: Cursor
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Summary
LocalStorageAssignmentShim's class field initializers forsizeand[Symbol.toStringTag]calledthis.getCache()before the constructor body assignedthis.localStorageKey. Per JS class semantics, field initializers run before the constructor body, sothis.localStorageKeywasundefinedandgetCache()readlocalStorage.getItem("undefined"). If that key held non-JSON data (e.g. from third-party scripts),JSON.parsethrew and the SDK failed to initialize.getCache()call during construction entirely, and also fixes a secondary bug wheresizewas a stale one-time snapshot that never reflected mutations.localStorage["undefined"]to a non-JSON value and verifiesLocalStorageAssignmentCacheconstruction does not throw.Jira: FFESUPPORT-610
Test plan
localStorage["undefined"]contains non-JSON — must not throwMade with Cursor