topic Re: How can I use a variable that is set in a function on an on event outside of the event? in ArcGIS JavaScript Maps SDK Questions

How can I use a variable that is set in a function on an on event outside of the event?

MichaelStranovsky — Wed, 02 Sep 2015 11:57:43 GMT

For instance:

featureLayer.on("selection-complete", function (result){

var pPoly = result.features[0].geometry;

});

console.log(pPoly);

the console returns undefined

Re: How can I use a variable that is set in a function on an on event outside of the event?

RobertScheitlin__GISP — Sat, 11 Dec 2021 08:59:39 GMT

Michael,

That when you use lang.hitch to maintain the scope of the function:

Be sure to require dojo/_base/lang

featureLayer.on("selection-complete", lang.hitch(this,function (result){
        var pPoly = result.features[0].geometry;
        //Now to will have access to the external var inside this function
}));
console.log(pPoly);

Re: How can I use a variable that is set in a function on an on event outside of the event?

MichaelStranovsky — Wed, 02 Sep 2015 12:11:24 GMT

Hi Robert,

Thanks for the quick response but I actually want to access the pPoly variable outside the onEvent after the function has been executed.

Michael

Re: How can I use a variable that is set in a function on an on event outside of the event?

TimWitt2 — Sat, 11 Dec 2021 08:59:42 GMT

You can define the variable outside your function , but just so you know the console.log will still return undefined since it will run before your selection. To test you would have to put the console.log into your other "on" function.

var pPoly;
featureLayer.on("selection-complete", function (result){
        pPoly = result.features[0].geometry;
});
console.log(pPoly);

Re: How can I use a variable that is set in a function on an on event outside of the event?

RobertScheitlin__GISP — Sat, 11 Dec 2021 08:59:45 GMT

Michael,

Well think of it the same way now that you have access to the outside scope of the function you just set an outside var that you create to the pPoly.

var pPoly;
featureLayer.on("selection-complete", lang.hitch(this,function (result){  
        pPoly = result.features[0].geometry;  
        //Now to will have access to the external var inside this function  
}));  
console.log(pPoly);

Re: How can I use a variable that is set in a function on an on event outside of the event?

MichaelStranovsky — Wed, 02 Sep 2015 12:43:05 GMT

Yeah I tried that and the console still reports undefined but if I place the console.log inside the event it return correctly. I need to use it though outside the event.

Re: How can I use a variable that is set in a function on an on event outside of the event?

RobertScheitlin__GISP — Wed, 02 Sep 2015 12:58:47 GMT

Michael,

And you are sure you use the code I had in my last post with the lang.hitch and the var outside the function?

Re: How can I use a variable that is set in a function on an on event outside of the event?

MichaelStranovsky — Wed, 02 Sep 2015 13:05:17 GMT

This is what I used:

var pPoly;

featureLayer.on("selection-complete", lang.hitch(this,function (result){

pPoly = result.features[0].geometry;

}));

console.log(pPoly);

Re: How can I use a variable that is set in a function on an on event outside of the event?

KenBuja — Wed, 02 Sep 2015 13:10:22 GMT

The question deals more with the progression of the code. Even though the line "console.log" is after the function section, it will get called first. The code inside that function will only occur when that event takes place (i.e. after the selection is complete on the feature layer).

Re: How can I use a variable that is set in a function on an on event outside of the event?

thejuskambi — Sat, 11 Dec 2021 08:59:48 GMT

I think I understand why Micheal is having problem, the console is executed before the event is raised. The selectFeatures method is a deffered method. so you need to you something like this.

var pPoly;

featureLayer.on("selection-complete", lang.hitch(this,function (result){
     pPoly = result.features[0].geometry;
})).then(function(){
     console.log(pPoly);     
});

Re: How can I use a variable that is set in a function on an on event outside of the event?

ReneRubalcava — Sat, 11 Dec 2021 08:59:50 GMT

You are having scope and order of execution issues.

To do what you want, you need to do something like this.

var pPoly;
function saySomething() {
  console.log(pPoly);
}
featureLayer.on("selection-complete", function (result) {
  pPoly = result.features[0].geometry;
  saySomething();
});

dojo/on does not return a Promise, so you cannot use then with it.

I'd recommend you look over this blog post

Take your JavaScript Up a Notch

And in particular look at closures.