node.js scope problems?

Question

I'm working on making a script with node.js for setting up my dzen2 in i3, and haven't really used node for anything like this before.

I need the geometry of the screen to start with, which I can get with something like this:

geometry = getGeo();

function getGeo() {
  var sh = require('child_process').exec("i3-msg -t get_outputs",
    function(error, stdout, stderr) {
      var out = JSON.parse(stdout);
      return out[0].rect; //this is the geometry, {"x":0, "y":0, "width":1280, "height":768}
  });
};

console.log(geometry);

console.log is logging undefined.

I'm not sure what the proper way to do this is, my brain is tired.

Robert Wilson · Accepted Answer · 2012-06-23 02:28:29Z

3

You can't return from the callback function since is async. Rather write another function and pass the callback object to it.

function getGeo() {
var sh = require('child_process').exec("i3-msg -t get_outputs",
    function(error, stdout, stderr) {
      var out = JSON.parse(stdout);
      getRect(return out[0].rect);
    });
};

function getRect(rect) {
    // Utilize rect here...
}

answered Jun 23, 2012 at 2:28

Robert Wilson

6691 gold badge14 silver badges30 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Rob Over a year ago

I've been working with so many different things, and just picking up coldfusion for work, that my brain is explody. Thanks, I remember how to write nodejs again.

Robert Wilson Over a year ago

haha..Glad it helped. You can accept it if it worked for you.

Ned Batchelder · Accepted Answer · 2012-06-23 02:20:25Z

0

You never return a value from getGeo(), you're returning a function from the anonymous function within it. But because of the async nature of the .exec() call, you can't return the value. You can put the console.log into the callback function, but that may not be where you want to use it in your real program.

answered Jun 23, 2012 at 2:20

Ned Batchelder

378k77 gold badges583 silver badges675 bronze badges

2 Comments

Rob Over a year ago

So what's the proper thing to do here? return sh from before

Ned Batchelder Over a year ago

node.js is based entirely on asynchronous programming with callbacks. You have to organize your code differently. Synchronous return values from functions are the wrong way to be thinking.

Collectives™ on Stack Overflow

node.js scope problems?

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related