Find numeric number from the text in javascript

Code :

    function isNumberKey() {

        var i = document.getElementById("product13").value.replace(/\D/g, '');
      
         document.getElementById("TextBox1").value = i;

    }


Use this function , it will take the value of textbox named ‘product13’  and it will find all number and assign to variable I and store its value in textbox1