How to use the nativescript-barcodescanner.available function in nativescript-barcodescanner

public scan(format?:string) {
        if (barcodescanner.available()) {
            barcodescanner.scan({
                formats: format,   // Pass in of you want to restrict scanning to certain types; AZTEC and MAXICODE formats dont work fine 
                cancelLabel: 'Stop scanning', // iOS only, default 'Close' 
                message: 'Go scan something', // Android only, default is 'Place a barcode inside the viewfinder rectangle to scan it.' 
                preferFrontCamera: false,     // Android only, default false 
                showFlipCameraButton: true,   // Android only, default false (on iOS it's always available) 
                orientation: 'portrait'      // Android only, optionally lock the orientation to either "portrait" or "landscape" 
            }).then(
                (result)=> {
                    console.log('Scan format: ' + result.format);
                    console.log('Scan text:   ' + result.text);
                    this.result = result.format + ' ' + result.text;
                },
                (error)=> {
                    console.log('No scan: ' + error);
                }

DemoAppModel.prototype.doCheckAvailable = function () {
    barcodescanner.available().then(
        function(avail) {
          dialogs.alert({
            title: "Scanning available?",
            message: avail ? "YES" : "NO",
            okButtonText: "OK"
          })
        }
    )
  };