How to concatenate a variable with string text for displaying as placeholder of an input [duplicate]

Question

I have this script for adding new input field when user click on a link with id of add:

$(document).ready(function() {
            var i = 1;
            $('#add').click(function(){
                i++;
                $('#dyanimc-field').append("<input type='text' name='tag_name[]' value='' class='form-control' id='tagInput' placeholder='Tag name'+i>");
            });
 });

Now this works fine and properly adds a new input field but I want the placeholder of this input to be showing the value of i variable next to the Tag name text.

So the inputs would have these placeholder:

Therefore I tried this placeholder='Tag name'+i> but this is wrong because it does not return any i variable value!

So how to concatenate a variable with string text for displaying as placeholder of an input correctly?