fix(RequestInit): restrict body type based on method to improve type safety #1953
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Thanks for the PR! This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged. |
saschanaz
reviewed
Mar 30, 2025
| interface RequestInit { | ||
| /** A BodyInit object or null to set request's body. */ | ||
| body?: BodyInit | null; | ||
| body?: 'GET' | 'HEAD' extends this['method'] ? never : BodyInit | null | null; |
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This won't work if method is a general string, e.g.:
function download(url: URL, method: string, body: any) {
return fetch(url, { method, body });
}Or method is lowercased or something weird like "gET" (this still works in browsers as the browser internally makes it uppercase). Actually not sure this would work even if method is GET/HEAD, can you add a unit test?
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Actually, when I think about it more, it seems that this is a missing feature in TypeScript. TS needs to have a Template Literal Type for case-insensitive matching.
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fixes #1678