losing global variable value

Question

This is for a gameing application I declare the variable skipnpc which is designed as an indicator that a non player character has used his turn and any AI code related to his behavior is skipped for a period of time. the problem I have is I am loosing the value of skipnpc somehow I indicated where in the console.log commands I issue is related to varaible scope but I don't understand how to fix it.

function npcMovement() {
    skipnpc = false;...
    sql4 = "SELECT id FROM game_moblist WHERE spawn_id =" + spawnid + " AND posx=" + parseInt(mobpathx[mobpathx.length - 1]) + " AND posy=" + parseInt(mobpathy[mobpathy.length - 1])
    connection.query(sql4, function (err, send, fields) {
        console.log("skipnpc pathing")
        io.sockets.emit('groupmoveresult', send, parseInt(mobpathx[mobpathx.length - 1]), parseInt(mobpathy[mobpathy.length - 1]))
        skipnpc = true
        console.log("skipnpc=true:" + skipnpc)
    });
    console.log("skipnpc = false:" + skipnpc)

Later I use

if (skipnpc==false){
  ...

before any further AI code is attempted

no this is run in node console its just a varriable I declared to trigger an if (skipnpc==true){...} — Shawn
– Shawn, Commented Aug 1, 2012 at 16:18
@kidwon not familiar with that but I think I'm not as from what I understand its for browsers. — Shawn
– Shawn, Commented Aug 1, 2012 at 16:22
Just a guess: could this be related to the async nature of the callback function? my guess would be that, either way you'll first see the console log false, but do you actually get to see the line skipnpc=true:true and then skipnpc=false:false? — Elias Van Ootegem
– Elias Van Ootegem, Commented Aug 1, 2012 at 16:22

Roest · Accepted Answer · 2012-08-01 16:23:43Z

2

connection.query is executed asynchronous. Thus you get to your final line here before it is done.

answered Aug 1, 2012 at 16:23

Roest

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5 Comments

Shawn Over a year ago

I don't see how that would cause this issue. But it doesn't explain how to get around the problem.

Roest Over a year ago

It's hard to tell from that code snippet. Is skipnpc defined somewhere else with var or is that the first occurence here. To make sure the rest get execute after the query finishes, arg stupid comment editor you can encapsulate the rest in a function and call it at the end of the query body.

Roest Over a year ago

I found that javascript in node is not so forgiving as in browsers. So "use strict" certainly helps to see problems before they do unexpected things.

Shawn Over a year ago

I defined skipnpc globally as in the snippet at the top.

Roest Over a year ago

node globals are not so global as you might expect, stackoverflow.com/questions/4140661/… has some interesting comments

ebohlman · Accepted Answer · 2012-08-02 09:50:35Z

1

To put it real simply, skipnpc is guaranteed to still be false by the time you hit your last console.log(...). You're not giving your connection.query(...) any time to execute before trying to look at its result. Anything that relies on the result of connection.query(...) has to be executed as part of the callback you passed to it; otherwise none of the results will have come in when you try to access them.

Asynchronous programming takes some getting used to. You might be able to reorganize your code using the async module and using its waterfall(...) method so everything doesn't wind up deeply nested. But you've got to realize that if you make an asynchronous call, your code will flow right past it.

answered Aug 2, 2012 at 9:50

ebohlman

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