How can I get the value from this variable inside function?

Question

I'm novice with javascript and I really don't know how can I get the "networks" value.

scanner.scan(function(error, networks){
   if(error) {
        console.error(error);
    } else {
        console.log(networks); << print the correct value
    }
});
console.log(networks) << print undefined

I just want to use "networks" outside function

Anyone could help me? Thanks!

@YosvelQuintero, yep, I know that, but how can I use "networks" outside function? — carloseduleal, May 15 '16 at 22:46
If `networks` variable is not previously defined, it will be hoisted, so that's why you get `undefined` — Yosvel Quintero, May 16 '16 at 00:05

score 0 · Accepted Answer · answered May 15 '16 at 22:07

Add a variable before the scan function and set the value inside the function:

var netValue = null;
scanner.scan(function(error, networks){
   netValue = networks;
   if(error) {
      console.error(error);
    } else {
      console.log(networks); << print the correct value
    }
});
console.log(netValue);

The final line still may not work though if the scanner.scan() function is an asynchronous call.

score 0 · Answer 2 · answered May 15 '16 at 22:08

You can create a global value networks, and update that from within the scan function:

var globalNetworks;

scanner.scan(function(error, networks){
    globalNetworks = networks;
    if(error) {
      console.error(error);
    } else {
      console.log(networks); << print the correct value
    }
});
console.log(networks) << print the correct value

I suggest that you read about how scope works in javascript: http://www.w3schools.com/js/js_scope.asp

score 0 · Answer 3 · edited May 23 '17 at 10:28

0

The reason you cannot get the value of networks is because it is wrapped in a closure, the value is only available inside that function. Go here to read more about closures:

How do JavaScript closures work?

To have access to it outside you can create another variable outside of the function and set that to variable to network inside the function:

var otherNetworks;
scanner.scan(function(error, networks){
   otherNetworks = networks;
   if(error) {
      console.error(error);
    } else {
      console.log(networks); << print the correct value
    }
   });
 console.log(otherNetworks) << print correctValue

edited May 23 '17 at 10:28

Community

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answered May 15 '16 at 22:10

omarjmh

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I already did it before, but it is only showing the global value, the variable is updated inside fuction, but does not persist its value outside. – carloseduleal May 15 '16 at 22:46
I highly doubt that, can you reproduce that in jsfiddle or jsbin? – omarjmh May 15 '16 at 22:48

score 0 · Answer 4 · answered May 15 '16 at 22:31

I already did it before, but it is only showing the global value:

var globalNetworks = "global"
var scanner = wifiscanner();

    scanner.scan(function(error, networks){
      globalNetworks = networks;
      console.log(globalNetworks) //displaying all the wlan0 networks available
      if(error) {
        console.error(error);
      } else {
        // console.log(networks);
      }
    });

    console.log(globalNetworks) // displaying global

btw, networks is a json

How can I get the value from this variable inside function?

4 Answers4