how to print cities based on zip code in javascript array?

I am trying to take zip code in input from user and trigger the on key up event which will populate the stores / cities available in that area, below is a code snippet for the same..

delivery.component.ts

zip: any = {
  "10020": ["A", "B" ],
  "20050":[ "X", "Y" ]
};

getCity = (theCurrentZip: any) => {
  let key = Object.keys(this.zip).filter(z => {
    return z.includes(theCurrentZip)
  }).values();
 
console.log("here",key);
 
}



onKeyUp(event: any){
    this.deliveryForm.patchValue({
      city: this.getCity2(event.target.value)
    })
  }

delivery.component.html

<form [formGroup]="deliveryForm" >
<div style="margin: 0 auto;text-align: left;">
      <div>
          <label>Zipcode:</label>
          <div><input id="zip" type="text" formControlName="zip" (keyup)="onKeyUp($event)"/></div>
      </div>
      <div>
        <label>City:</label>
      <input id="city" type="text" formControlName="city">
      </div>
  </div>
</form>

getCity = (theCurrentZip: any) => {
  return this.zip[theCurrentZip];    
}

If I didn't miss anything important it should do the work.