TypeError: Cannot convert undefined or null to object javascript

Question

I am getting an error when trying to delete object. Currently there is no data as it is added through out other code. May issue is that I may need to delete the data if it exist. I guest I need a way to check if the data exist before deleting

Error message: TypeError: Cannot convert undefined or null to object

The error is coming from this line: delete rooms?.[roomId]?.[socket.id];

interface IDevice {
    deviceId: string;
    deviceName?: string;
    socketId: string;
    isReconnecting?: true | false;
}

const rooms: Record<string, Record<string, IDevice>> = {};

if (typeof rooms?.[roomId]?.[socket.id] !== 'undefined' && rooms?.[roomId]?.[socket.id] !== null) {
     delete rooms?.[roomId]?.[socket.id];
}

What line is the error for? Also, you shouldn't need the optional chaining within the if, as you have already checked that the properties exist. — Darryl Noakes
– Darryl Noakes, Commented Jan 19, 2023 at 20:17
error comes when I run this line: delete rooms?.[roomId]?.[socket.id]; — Jerry Seigle
– Jerry Seigle, Commented Jan 19, 2023 at 20:25
A simpler reproduction of the issue would be useful as well. delete null and delete undefined work fine for me. — JBallin
– JBallin, Commented Jan 19, 2023 at 20:28

Moritz Ringler · Accepted Answer · 2023-01-20 08:48:26Z

0

Just remove the ?. in the delete: delete rooms[roomId][socket.id]; It tells typescript that the value might be undefined (and you cannot do delete undefined, which is the error you get). You have already checked that that the value exists, so it's fine.

edited Jan 20, 2023 at 8:48

answered Jan 19, 2023 at 22:03

Moritz Ringler

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