component.html

//HTML
<input type="text" [(ngModel)]="_num"/>
<ul>
	<li *ngFor="let item of numList | numFilter:_num">
		{{item.po}}
	</li>
</ul>

<p>_num:{{_num}}</p>

ngFor_pipe.ts

//TS
import { Component, OnInit } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { FormBuilder, FormGroup, FormControl, Validators } from '@angular/forms';

import { NumFilterPipe } from '../num-filter.pipe';
@Component({
  selector: 'app-num',
  templateUrl: './num.component.html',
  styleUrls: ['./num.component.css'] 
})
export class NumComponent implements OnInit {

	_num;
	numList = [
		{po:'500123'},
		{po:'94938'},
		{po:'7857'}
	];	

  constructor() { }

  ngOnInit() {
  }

}

num-filter.pipe.ts

//ng g pipe numFilter
//num-filter.pipe.ts
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'numFilter'
})
export class NumFilterPipe implements PipeTransform {

  transform(numList: any, _num: any): any { 
    if(_num === undefined) return numList;

    return numList.filter(item => {  
    	console.log(item.po.includes(_num));
    	return item.po.includes(_num); 
    })
  }

}