Append text to input field

If you are planning to use appending more then once, you might want to write a function:

//Append text to input element
function jQ_append(id_of_input, text){
    var input_id = '#'+id_of_input;
    $(input_id).val($(input_id).val() + text);
}

After you can just call it:

jQ_append('my_input_id', 'add this text');

There are two options. Ayman's approach is the most simple, but I would add one extra note to it. You should really cache jQuery selections, there is no reason to call $("#input-field-id") twice:

var input = $( "#input-field-id" );
input.val( input.val() + "more text" );

The other option, .val() can also take a function as an argument. This has the advantange of easily working on multiple inputs:

$( "input" ).val( function( index, val ) {
    return val + "more text";
});

    $('#input-field-id').val($('#input-field-id').val() + 'more text');

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<input id="input-field-id" />