Javascript: unshift key value array

Question

I'm trying to add a specific item on the front of an array but I can't work out how to do this? I know you do it with unshift, but I'm not sure how to do it with a key value array?

var outgoingHeaders = {
    "send_client_version": 1,
    "send_auth_ticket": 5
};

function sendPacket(packetName, packetData) {
    const packetId = outgoingHeaders[packetName];
    const packetArray = {'packet_id' : packetId };
    // TODO: Add packetArray at the start of packetData
    socket.send(JSON.stringify(packetData));
}

Example of calling it...

sendPacket('send_auth_ticket', {
    'auth_ticket' : authTicket,
});

Is `packetData` really an array? From what you wrote it seems like it's an object, and in that case you can't really control the order of the items. — klh, Jan 19 '18 at 21:39
Not sure if this is the source of confusion but just in case: unlike some programming languages there is no "key value array" (or what some call an associative array) in Javascript. — luckyape, Jan 19 '18 at 21:56
So I'm guess I'm asking how to do it with a key value object, I'm sorry if it was called something else but I usually call it a key value array, I apologize. — regu, Jan 19 '18 at 22:05
Then "unshifting" and "order" are inappropriate too, since objects don't have an order. Do you merely want to add the key-value pair into the object…? — deceze, Jan 19 '18 at 22:07
I just want to ensure that packet_id is the first item in the json string when sent to the server. — regu, Jan 19 '18 at 22:08
And that ain't gonna happen. Objects. Have. No. Guaranteed. Order. Neither in Javascript nor JSON. — deceze, Jan 19 '18 at 22:09

Rogerio Moura · Answer 1 · 2018-01-20T01:06:18.867

0

You can use concat array method, like:

function sendPacket(packetName, packetData) {
  const packetId = outgoingHeaders[packetName];
  const packetArray = [{'packet_id' : packetId }];
  const data = packetArray.concat(packetData);
  socket.send(JSON.stringify(packetData));
}

Nice thing about this, you keep the immutability of your variables :)

edited Jan 20 '18 at 01:06

answered Jan 19 '18 at 21:37

Rogerio Moura

1
2

Apparently concat doesn't exist? – regu Jan 19 '18 at 21:54
packets.js:12 Uncaught TypeError: packetArray.concat is not a function – regu Jan 19 '18 at 21:54
packetArray need to be a array. I edited there :) – Rogerio Moura Jan 20 '18 at 01:06

score 0 · Answer 2 · answered Jan 19 '18 at 21:40

Since you did not provided any JSON sample this is a suggestion:

var outgoingHeaders = {
  "nameee" : 33
}


function sendPacket(packetName, packetData) {
    var packetId = outgoingHeaders[packetName];
    var packetArray = {'packet_id' : packetId };
    // TODO: Add packetArray on the front of packetData
    packetData.unshift(packetArray);
    console.log(JSON.stringify(packetData, null, 4));
}




sendPacket("nameee", [{'packet_id' : 14 }, {'packet_id' : 5 }])

I've updated my question to make it more clear. – regu Jan 19 '18 at 21:59 — regu, Jan 19 '18 at 21:59

Javascript: unshift key value array

2 Answers2