Ion-input Currency Format Help

Ionic Framework Ionic Angular
1

I’m currently using an ion-input element to retrieve input from the user (specifically amount in dollars USD), however I am having a difficult time trying to figure out the best way to approach this where it restricts the amount of decimals and normalizes the amount (i.e $5.0 → $5.00 or $5.201 is not valid and input past $5.20 is not allowed).

Here is my relevant code:

create-listing.page.html

<ion-input type="text" [(ngModel)]="listingPrice" (keyup)="listingPriceValidation($event)" debounce="0"></ion-input>

create-listing.page.ts

listingPriceValidation(event: any) {

      // const pattern = new RegExp('^[+-]?[0-9]{1,3}(?:,?[0-9]{3})*\.[0-9]{2}$');
      const pattern = new RegExp('^[+-]?[0-9]{1,3}(?:,?[0-9]{3})*(?:\.?([0-9]{1,2})?)?$')

      let userInput = this.listingPrice;
      let output = "";

      if ( pattern.test(this.listingPrice) === true ) {
        let holdingNumber : number = 0;
        holdingNumber = +userInput;
        let output = holdingNumber.toFixed(2);
        this.listingPrice = output
      } else {
        event.preventDefault();
      }
    }

This code works in that it adds decimals when someone types in a whole number initially, but the UX isn’t really good since it makes the user have to highlight a certain place to edit the dollar amount. Also, the regex for some reasons accepts any input at the “.” place.

Does anyone have any suggestions on how to improve this?