1var element = document.getElementById("oldID");
2element.id = "newID";

1element = document.querySelector("#id");

1var element = document.getElementById("YourElementId");
2var value_element = document.getElementById("YourElementId").value;

1var element = document.getElementsByTagName("div")[0];
2var id = element.id;

1document.getElementById("IdGoesHere");

1var x = document.getElementsByClassName("anchors")[0].id;