What is the meaning of this error "Declaration of instance field not allowed after declaration of instance method."

In my Angular2 project I receiving this error:

"Declaration of instance field not allowed after declaration of instance method. Instead, this should come at the beginning of the class/interface. (member-ordering)"

I would like to understand how to resolve this and why I'm getting this.

The error is related to the private function in the next code:

export class HomeComponent implements OnInit {
public error: string;
public shirts = [];


constructor(public rest: RestService,
            public scService: ShoppingCartService,
            public snackBar: MdSnackBar) {
}


ngOnInit() {
    this.rest.getAll().subscribe((r: any) => {
        this.shirts = r;
    }, error => {
        this.error = 'Opps there\'s some error';
    });

}

addToCart(shirt: any) {
    this.scService.add(shirt);
    this.showSnackMessage('Added to Chart List');
}

showSnackMessage(message: string) {
    this.snackBar.open(message, null, {
        duration: 1000
    });
}
//Here the error is showed
private sizeScore = {
    'string': -1,
    s: 0,
    m: 1,
    l: 2,
    'x-large': 3,
};

sortData(sort: Sort) {
    const data = this.shirts.slice();
    if (!sort.active || sort.direction === '') {
        this.shirts = data;
        return;
    }

    this.shirts = data.sort((a, b) => {
        let isAsc = sort.direction === 'asc';
        switch (sort.active) {
            case 'colour':
                return compare(a.colour, b.colour, isAsc);
            case 'size':
                return compare(this.sizeScore[a.size], this.sizeScore[b.size], isAsc);
            default:
                return 0;
        }
    });
}
}