1You can apply any one approach:
2
3$("#Input_Id").change(function(){   // 1st
4    // do your code here
5    // When your element is already rendered
6});
7
8
9$("#Input_Id").on('change', function(){    // 2nd (A)
10    // do your code here
11    // It will specifically called on change of your element
12});
13
14$("body").on('change', '#Input_Id', function(){    // 2nd (B)
15    // do your code here
16    // It will filter the element "Input_Id" from the "body" and apply "onChange effect" on it
17});

1//for imput field given in HTML
2
3<input type="text" id="myid" class="myclass" >
4  
5// Using ID to find value
6  
7$("#myid").val();
8
9// Using Class to find value
10
11$(".myclass").val();
12 

1$('selector').val('new value');

1    $("button").click(function(){
2  $("input:text").val("Glenn Quagmire");
3 })