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let abort: ( WebAPI.FileAPI.writableStream<'w>, ~reason: JSON.t=?,) => Promise.t<unit>
let close: WebAPI.FileAPI.writableStream<'w> => Promise.t<unit>
let getWriter: WebAPI.FileAPI.writableStream< 'w,> => WebAPI.FileAPI.writableStreamDefaultWriter<'w>
let make: ( ~underlyingSink: WebAPI.FileAPI.underlyingSink<'w>=?, ~strategy: WebAPI.FileAPI.queuingStrategy<'w>=?,) => WebAPI.FileAPI.writableStream<'w>