如何使用 socket.io 向客户端发出未定义/空值？

Question

I recently discovered that the socket.io parser seems to strip keys with undefined/null values from emitted data objects. This is undesirable as i'm trying to use these values to clear information from my views.

Does anyone know a work around for this? The API allows you to provide your own parser but i'd prefer not to go down that route or alter the defualt parser ( socket.io-parser ).

Answer 1

I haven't seen this specific behavior. A quick workaround could be to always send a boolean parameter isUndefined or isNull and check it at the other end.

Answer 2

Same behaviour is observed on JSON.stringify() (which I suspect socket.io is using) and also undefined is not a valid JSON token.

You could replace undefined with whatever you want before sending. Either as null or as some custom string and do the necessary checks on the other end

const dataToEmit = { something: undefined };

const replaceWith = null;
const s = JSON.stringify(dataToEmit, (k, v) => v === undefined? replaceWith : v );
const dataParsed = JSON.parse(s)

socket.emit("channel_name", dataParsed);