Angular 4 Long file name

long-file-name.pipe.ts

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

/*
 * Format long file name
 * Max length, default is 100
 * Usage:
 *   filename | longFileName:maxLength
 * Example:
 *   {{ 'demo file name long at here, this is long file name omg please try input now.txt' |  longFileName:40}}
 *   formats to: demo file name long ...se try input now.txt
*/
@Pipe({
  name: 'longFileName'
})
export class LongFileNamePipe implements PipeTransform {

  public transform(filename: string, maxLength: number = 100): any {
    if (filename === null) {
      return filename;
    }
    let midLength = (maxLength / 2).toString();
    let pattern = '^([a-zA-Z\\s,\\-\\_\\.]{' + midLength + '})(.*)([a-zA-Z\\s,\\-\\_\\.]{' + midLength + '})$';
    let regex = new RegExp(pattern);
    return filename.replace(regex, '$1...$3');
  }

}