How to use Global variable inside cordova-sunmi-inner-printer default functions

[saravanacs]

I'm using cordova-sunmi-inner-print for printing sunmi v1 thermal printer device. More predefined functions here like printerStatusStartListener(), printerInit(),printstring() and so on. My doubt is globally defined variable not using inside predefined function like printerStatusStartListener().

Not alert any messages call and inside printerStatusStartListener() isPrinterValid variable type is 'any'. But, outside function check type is 'boolean'.

So, please suggest how to use global variable inside sunmi-inner-printer function or suggest any other ways

my code is here,

declare var sunmiInnerPrinter: any;
public isPrinterValid:boolean = true; // globally assign true
sunmiInnerPrinter.printerStatusStartListener(function (onSuccess) {
alert("On Success : "+ JSON.stringify(onSuccess))
if (onSuccess != undefined && onSuccess.action == PrinterConstants.NORMAL_ACTION) {
alert("success")
this.isPrinterValid = true; // condition is valid update 'true'
alert("success Value :"+this.isPrinterValid) // not calling alert
}
else {
alert("failure");
this.isPrinterValid = false; // condition is false, update 'false'
alert("failure Value :"+this.isPrinterValid) // not calling alert
}
}