[Solved]-D3 invalid character in element-d3.js

The reason was that you can't start elements with numbers. I had to do:

var responseNode = group.append("n"+id).attr("fill","black").attr("x", 15).attr("y", 15).attr("width", 190).attr("height", 90);

to get it to work.

I believe that I understand your problem.

D3's .append():

If the specified type is a string, appends a new element of this type (tag name) as the last child of each selected element, or the next following sibling in the update selection if this is an enter selection. [...] This function should return an element to be appended. (The function typically creates a new element, but it may instead return an existing element.

Why .append() work fine if you pass 'foo'? Because D3 append a custom tag element. If you see in your console I'am sure that you will see <foo>...</foo>

Why .append() work wrong if you pass '5802bc044f6313c1097de4a2'? A custom tag element can't start with a number. You don't use _id, you should try to find another pattern for identify your element.

I hope that helps