JSFiddle - React, Tailwind, and code Playground

HTML

<div ng-app="myApp" ng-controller="myCtrl">

  A_Number:
  <input type="number" step="1" ng-model="A_Number">
  <br> Display (A_Number): {{A_Number}}
  <br> square: {{square}}
</div>

JavaScript

var app = angular.module('myApp', []);
app.controller('myCtrl', function($scope) {
  $scope.square = 0;
  $scope.$watch('A_Number', function(newValue, oldValue) {
    {
      if (!isNaN(newValue)) {
        $scope.square = $scope.A_Number * $scope.A_Number;
      }
    }
  });
});