appendChild function not working

//I am creating dynamic form using java script

,Here is my js file ,i want to know logic behind below code with comment

  var element=document.createElement("input");
    element.setAttribute("type","text");
    element.setAttribute("placeholder","*Name");
    element.setAttribute("name","name");
    var namefield=document.getElementById("namefield");
    namefield.appendChild(element);

    var element11=document.createElement("br");
    var br=document.getElementById("namefield");
    br.appendChild(element11);//not working
    br.appendChild(element11);//not working`enter code here`

    br.appendChild(document.createElement("br"));
    br.appendChild(document.createElement("br"));//its working,i cant understand reason behind it, i want to know actual reason behind it