orderBy pipe in Angular2

orderBy.ts

@Pipe({
  name: 'orderBy'
})
export class OrderByPipe {
  transform(value: Array<any>, args: any[]): any {
    let field: string = args[0];
    if(value==null) {
      return null;
    }
    if (field.startsWith("-")) {
      field = field.substring(1);
      if (typeof value[field] === 'string' || value[field] instanceof String) {
        return [...value].sort((a, b) => b[field].localeCompare(a[field]));
      }
      return [...value].sort((a, b) => b[field] - a[field]);
    }
    else {
      if (typeof value[field] === 'string' || value[field] instanceof String) {
        return [...value].sort((a, b) => -b[field].localeCompare(a[field]));
      }
      return [...value].sort((a, b) => a[field] - b[field]);
    }
  }
}

I just switched it to take one string argument "field" since I needed only to sort by one attribute, only.

Used it this way:

<li *ngFor="let item of collection | orderBy: orderByModel" > ... </li>

Where "orderByModel" is dynamically changing.

Here is the updated pipe:

import { Pipe, PipeTransform }   from '@angular/core';

@Pipe({name: 'orderBy'})
export class orderByPipe implements PipeTransform {
  transform(value: Array<any>, field: string): any {
    if(value == null) {
      return null;
    }
    if (field.startsWith("-")) {
      field = field.substring(1);
      if (typeof value[field] === 'string' || value[field] instanceof String) {
        return [...value].sort((a, b) => b[field].localeCompare(a[field]));
      }
      return [...value].sort((a, b) => b[field] - a[field]);
    }
    else {
      if (typeof value[field] === 'string' || value[field] instanceof String) {
        return [...value].sort((a, b) => -b[field].localeCompare(a[field]));
      }
      return [...value].sort((a, b) => a[field] - b[field]);
    }
  }
}

The pipe works fine with the last change. Thanks!!