How to prevent Angular Material mat-select change option?

Question

<mat-form-field appearance="fill">
  <mat-label>Favorite food</mat-label>
  <mat-select [formControl]="topFormControl" [(value)]="topSelectValue">
    <mat-option *ngFor="let food of foods" [value]="food" >
      {{food.viewValue}}
    </mat-option>
  </mat-select>
</mat-form-field>

  ngOnInit(): void {
    this.topFormControl.valueChanges
      .pipe(
        startWith(this.topFormControl.value),
        pairwise()
      ).subscribe(
        ([old, cur]) => {
          if(
            //cur.value === 's'
          ){
            //prevent user select the option, force mat-select still shows the old option.
          }
        }
      );
  }

  foods: Food[] = [
    { value: 's', viewValue: 'Steak' },
    { value: 'p', viewValue: 'Pizza' },
    { value: 't', viewValue: 'Tacos' },
  ];

Is there any solution when user select Steak in Favorite food, prevent mat-select to show Steak but keep the old option?

Thanks a lot.

Answer 1

I corrected some extra properties... such as num.value, e.value, .toString

  function onOpen() {
      var ui = SpreadsheetApp.getUi();
      // Or DocumentApp or FormApp.
      ui.createMenu('Bedrock')
          .addItem('Hyperlink Phone', 'menuHyperLinkPhone')
          .addToUi();
    }
    
    function menuHyperLinkPhone() {
      SpreadsheetApp.getUi() // Or DocumentApp or FormApp.
      
      var ss = SpreadsheetApp.getActiveSpreadsheet();
      var activeCell = ss.getActiveCell();
      var num = activeCell.getValue().toString();
    
      if (num.length == 0){
        ss.toast("Length is 0.")
        return;
      }
    
      if (num.indexOf("ctrlq.org") !== -1) {
        return;
      }
        
      if (num.length == 10) {
        console.log(num)
        console.log(typeof num)
        ss.toast("Length is 10.")
        activeCell.setValue('=HYPERLINK("https://ctrlq.org/call/'+num+'","'+FormatPhoneNumber(num)+'")');
      }
        
      if (num.length > 10) {
        ss.toast("Length is greater than 10.")
        activeCell.setValue('=HYPERLINK("https://ctrlq.org/call/'+num.substring(0,10)+'","'+FormatPhoneNumber(num)+'")');
      }
    }

function FormatPhoneNumber(number) {

  var num = number;
  var length = num.length;

  if(length == 0){
    return num;
  }

  if(length == 10){
    var areacode = num.substring(0,3)
    var prefix = num.substring(3,6)
    var lastfour = num.substring(6,10)

    num = "("+areacode+") "+prefix+"-"+lastfour;

    return num;

  }

  if(length > 10){
    var areacode = num.substring(0,3)
    var prefix = num.substring(3,6)
    var lastfour = num.substring(6,10)
    var extension = num.substring(10)

    num = "("+areacode+") "+prefix+"-"+lastfour+" ("+extension+")";

    return num;

  }

}