setInterval and its first argument and socket.io emit

Asked Aug 03 '17 at 08:47

Active Aug 03 '17 at 08:47

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I just noticed a strange behavior while using setInterval. I'm using setInterval to request the server to send data every 2 seconds, and this is what I quite naturally proceeded to do:

this.socketInterval = setInterval(this.socketio.emit, 2000, 'persist'); // didn't work

I thought it would do the trick as,

this.socketio.emit('persist');

had worked. Instead it threw an error

Uncaught TypeError: Cannot read property 'push' of undefined

I got it to work by encapsulating it within a function, but I am still curious about why simply passing this.socketio.emit as first argument didn't work.

this.socketInterval = setInterval(p => this.socketio.emit(p), 2000, 'persist'); // works!

asked Aug 03 '17 at 08:47

いちにち

2

`this` is wrong within `emit`. Instead: `setInterval(this.socketio.emit.bind(this.socketio), 2000, 'persist')` – T.J. Crowder Aug 03 '17 at 08:50
Or with ES2015+: `setInterval(() => this.socketio.emit('persist'), 2000)` – T.J. Crowder Aug 03 '17 at 09:02

setInterval and its first argument and socket.io emit

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